Here's an alternative to coffee grinders and the air dubbing mixers.
I have a pair of carding brushes that I use to mix dubbing. Works better than any coffee grinder or air system for long fibers that tend to wrap them selves around the grinder blades. They are used to pull apart and align wool from sheep and llamas so the fibers can be spun into wool yarn on a spinning wheel.
They are great for small amounts of dubbing and you can titrate the amounts of different fur to get just the mixture you want. You want a small amount of a specific color to try? No Problem!
Dog brushes can be used but carding brushes work much better and faster.