Honey is the most important ingredient in mead (duh!), and using quality honey is the first step to making quality mead. But how do we get it? Where can I find it? And what is it?
Let's start with what quality honey is. I'm going to say that unheated, minimally filtered, fresh honey is the best; we'll call this "raw" honey. Having said that, not all "raw" honey sold meets this definition: many products labelled as such have been heated and filtered beyond what I would prefer. It is very important to get to know your beekeepers for this reason, but I'll get to that in a bit. You should also be aware that not all honey that matches my definition tastes good, some types of honey, from certain vintages or floral sources, just tastes downright bad. Some honeys taste great, but make bad mead. And some honeys taste terrible and make great mead. Some need to be blended with other types and end up being very interesting, or they can ruin a batch. This is all part of the risk in using exotic honeys, or trying new honeys that you haven't had before; and there is very little advice anyone can give for many of these as they may work great sometimes and turn out bad other times, it's a matter of personal taste.
Where to find honey Start local; it will be fresh and you may know exactly where it came from. It also give you a sense of "terrior" in your mead making (sorry to use the controversial wine term, but it's the best way to get the idea across). I will also say that small does not always mean better; a large honey producer who cares about his product is better than the small "honey guy" who has no concept of quality.
Your first stop should be any of the several homebrew/meadmaking/winemaking forums. Post something saying where you are and try finding mead makers in your area. You can also try your local homebrew shop; ask if anyone makes mead in the area, they might also have local honey and a quick conversation with the owner may get you somewhere. Next stop is the USDA honey board locator. While it will not list all the producers in your area, you are bound to find some. They usually list some form of contact information (website, email, phone, etc.) that you can use to contact the producer. The site also lets you see what the common honeys produced in your state are.
Local farmers market are your friends when it comes to finding local producers. Any good farmers market should have a honey booth (or several), and if it doesn't try another one. Try as many as you can drive to, and try them several times a year as some honey producers don't show up year round. When you do find a honey booth, try every sample they'll let you have, if you have to give the guy 5 bucks/quid/euro/whatever do it.
The next thing to try is a local Whole Foods, health food store, or other hippie store (no offense, again best word for the job). Go to their honey section (usually near maple syrup) and look for any products labelled as local, or start looking at the containers to find the producers address and try to find one that's near your area. Buy some honey from the producers you find and start tasting it; if it's good, try to contact the producer. If you don't have a hippie store in your area, move (seriously, it's probably a bad indication no matter what you views are). Local supermarkets (the publix/target type, not Walmart) sometimes carry local honey as well, try to find some and contact the producers.
After this, if you can't find anything local your in a tough spot. You can try contacting your local university extension office and see if they have any registry of apiarists, or a local club. Even a hobby beekeeper can produce a decent surplus that you can buy or trade some mead for. Don't be afraid to stop at roadside honey venders either, they usually have their own hives or buy from someone local.
Honestly, if you can't find a local beekeeper your either not looking hard enough, or your in a place that humans should not live. However, there are a number of alternatives.
Many large scale apiarists have websites and commonly ship honey cross-county. Beefolks has high quality honey at a good price and can ship you many different varieties. Dutch gold, while limited in offerings and processing their honey a little too much for my preference, is another such company.
The last resort should be generic store honey. Costco's, BJ's and Sams club all have large containers of honey. I find Costco's to be the best of the three, but all are cheaper than regular supermarket honey.
Befriend your beekeeper(s) While not necessary, it is a very good idea to get to know your beekeeper. He'll let you know what crops aren't good in a certain year, and can point you toward some interesting rare honeys he might get. After you've tasted his honey selection and deemed it worthy, bring a bottle of mead and offer it to him, if he refuses for reasons other than religious or philosophical, check to make sure he's not a Dalek, cyberman, or other "bad guy". Often times a reduction in price can come with buying a certain volume or bartering with mead, and a good level of trust in the person supplying your most precious ingredients is not something to shy away from.
Diversify The best strategy for any investment portfolio, and trust me, mead making is an investment, is to diversify your sources. I get most of my honey from two local sources, one in central Florida (Webbs honey) and one in south Florida (Smak attack, or something like that) by me. The first is a larger producer who can sell by the barrel, and I get great consistency from him. The latter is very small and gets certain rare honeys that are hard to come by. There is a price difference, but there's also a difference in hive locations which allows for more complex meads via blending (either within varietal boundaries or not). I have also bought from larger online producers, and roadside vendors, and even used generic bulk honey for some melomels (though I tend not to anymore). The more options you have, the more creative you can be, and the better bargain you can get. I think the strategy of "infinite diversity, in infinite combinations" is a very good one to adopt when it comes to honey varieties and mead making (is my geek showing?).