djeucalyptus

I usually purchase them at the University of Oregon Bookstore Art Supply section. I've seen them at other craft stores like Michael's, as well as specialty art supply stores. They're usually found in the drafting/illustrating pens section, along with Copic markers, MicroLiners, etc. I looked and found some HereHere. Looks like they may be getting harder to find on the whole, but if you call around, I'd bet you could find some somewhere.