I've got the Lyman Black Powder Handbook by Sam Fadala. I couldn't say whether or not it's the best, it's just the one that I have.
As far as supplies go, whew, there are a ton of places out there. The only BP cartridge loading that I do is .38/.357 and I get supplies from Buffalo Arms (www.buffaloarms.com
) because, although they're 400 miles away, we're both in Idaho, so it's about as local as I can buy.