Not a wide selection, but great prices on what they do carry, here:

Fly Tying Furs, Home of Coffins Creek Furs - We Buy, Sell, and Process Fly Tying Furs and Feathers

Good quality dry fly hackle capes are never cheap, but at least Charlie Collins does offer a very good value and a wide range of colors. He also throws in the saddle from the same rooster for free when you buy the cape.

Collins Hackle Farm

And it's always worth checking to see what Mike Hogue has in stock: