Whats known as a file card which is basically a big wide short haired wire brush. I seem to remember doing something with french chalk to files back when I did O level metalwork (It was a long time ago!)
There is a product called 'file carding' which looks like lines of staples driven up through a piece of canvas so that the points form a sort of 'bed of nails'. This can be used to clean file teeth - best mounted on a small piece of board.
Sometimes a the edge of piece of the 'hard brass' rubbed across the file in the direction of the lines of teeth will shift some of the bits.
For the really obstinate bits then picking at them with a scriber is really the only way to go, but does not do much for the teeth or the scriber
A better way is to stop the teeth from 'pinning' in the first place. Take a piece of ordinary soft chalk as used in schools(hard french chalk can be used but more expensive) and rub this into the file face before use. This has the effect of filling in the tooth pockets with chalk whilst still allowing the tooth to cut. Because the pocket is now full of chalk means that it can't fill up with aluminium which bounces out. You will need to keep doing this of course.
Also worth doing with most metals particularly when the file is very new and sharp.