Erick,
several people make em. You can do a search and check out some of KrustKlimbers handcarved open reeds. Alot of guys on here make howlers from cowhorn and carve the open reed portion of the howler from the solid part of the horn. Antler also.
In short, you can make a open reed out of any material. Some people like wood and some like plastic etc.
Hmmm...maybe Ill make one out of coyote legbone /ubbthreads/images/graemlins/laugh.gif