I don't have a commercial source, but I just put an old pencil in my drill (you could easily use a belt sander also) and sand it down to the thickness I want, then I cut it to the length I want (I usually make 2 or 3 out of a used pencil). Since you can pick up a pencil just about anywhere, it doesn't really cost anything. If you started with new pencils, you could probably make 5 out of each, so 10 pencils later, plus your time, and your set.

Unfortunately for Doug, this method is a tad labor intensive for his purposes, but it works great for my tiny kits.

Greg