I did a post a few weeks ago with the scale blanks I buy off eBay. For 6" x 1 1/2" bone:
Bleached Bone Scales 6” x 1 1 2” x 3 8” Pair Knife Making Slabs 5404 206 204 | eBay
And for 6" x 1 1/2" horn:
Buffalo Horn Scales 6” x 1 1 2” x 3 8” Pair 5404 205 204 | eBay
You might search the seller for different material but I think they quit having the micarta in that size. They used to have a selection but this is who I use.