I have tried buying a piece of leather to make a saddle out of it, and I could not find anyone who would sell me a small piece. They would sell me a large piece, that is, a whole side; which is, well, about the size of one side of a cow. It's enough to make quite a few saddles. Now I suppose Brooks may have ways of buying partial hides that I don't have, and they may well prefer to make saddles from the butt of the cow, where the best leather is; but frankly I suspect they, too, have to buy their leather by the side, or by the hide; then what do you want them to do with the rest of it? I suppose they could charge a different price, depending where the leather came from... and maybe they do. But using the whole hide is the environmentally responsible thing to do.
Try a Tandy Leather retail shop. They usually have a table of remnants out.