I've seen up to a 23 tooth gear, but the teeth are so thin, they have a shorter life.
If I recall correctly the highest tooth-count available from Ford Motor Co. was 21; the 23 tooth piece, which I believe was actually a Chrysler/Dodge product, which became popular in the FOX Mustang era, but never worked properly for long as yes the individual gear tooth was thin, but it also is at the wrong angle.
But, the vendors sold the shyte out of 'em anyway!
Scott.