So far everybody has talked about the coffee grinder
idea (with one new twist for me: reverse the blades, so
they lead with a dull edge).

But you mentioned that Frank mentioned the carding comb.
I got mine at a ladies sewing store--one that specialized
in looms and yarn weaving--you know, the kind of store
where you see beautiful makeupless women with batik
clothing bare legs and sandles, even in winter. So anyway, what
I'm talking about is two plastic handled paddles with
red rubber backing, that has hundreds of short and slightly
bent wires sticking out. I take the output from the coffee
grinder and put that between the cards for a few strokes.
Then all the fibers are lined up, like fundamentalists
before the firing squad. Makes a better dubbing that way.