You could make your own easily enough. Put an open hook in a block of wood and on the other end put a crank handle attached to an English style hackle plier.
To use it, string a wire (copper, silver, or gold) between the hackle plier and the open hook. Put the dubbing material on the block, and crank the handle until is forms a dubbing brush. You can also make it out of a low rpm electric motor (no higher than 40 rpm though) and let the motor do the work for you.
You could also use a rotary tying vise to produce dubbing brushes. Just remember to use wire because it will stay together after the dubbing brush is made.
Personally, I'll either split the tying thread9 yes, you can split 8/0 thread), or use floss and split it to produce a dubbing loop. This is far easier than making a loop of thread, just as strong, and if formed from floss (or UNI Stretch), it has a more intense color saturation. Syd Glasso tied his flies with this technique. This technique will also cause you to get very good at using just the right amount of dubbing to form the body with none left over.