I use Burl Source a lot and also Arizona Ironwood. Burl Source has some really cool woods and the pieces are bigger, so you can often get 1 or 2 Wa handles and sometimes a ferrule or two out of his bigger blocks, or 2 Westerns and some ferrules/bolsters out of the single block, depending on the size.
Great stuff from Arizona Ironwood and they have lots of different colors on hand and a ton of pieces to choose from. I just got 3# of small chunks of Ironwood Burl that will make great ferrules for Wa handles, prob enough for 15-20 Wa handles. They have good specials on more plain Ironwood, too. It has some figure and streaking, but it's not the crazy expensive burl.
Pins, I get them from Jantz or Texas Knifemakers Supply.
I like Maple Burl and Box Elder Burls (dyed) the best I think. Both are easy to work and have nice figure. Amboyna Burl is a pain to work, burns easily and reminds me of Ironwood when working it, but harder. But it looks nice when it's finished