I have bought wool at many of the places above as well as Heavens-to-Betsy.com. When I wanted to try braiding rugs, I was able to get some inexpensive wool through eBay, I think it was remnants from uniform making or something like it. Thrift store hunting is fun but of course variable...when I used to do it, there was a lot of wool available and you could pick and choose (I used skirts only, as there is more fabric without seams), but I can see that wool appliqué is getting more popular so it will be harder to find.
I bought a large quantity of undyed wool from Dorr Mills and dyed it myself, which was a lot of fun. Would you consider doing that? If you want small quantities (I haven't seen the pattern) you can felt and dye them simultaneously on top of the stove using food coloring - safer and easier (btw, I have done quite a bit of yarn and and fabric dying and the most toxic of all the chemicals ar those used for natural dying).
If you have any questions or if you need some fabric, you could pm me, I have a lot left from other projects kthat you could have.