This shouldn't be hard, all you need is a correct diameter seat post, the wedge assembly out of an old, long stem, and a cap with a hole in it. Cut a 45* angle in the bottom of the post, assemble, and call it a day. If you want to get really fancy you could weld the cap on. If you can't find an old stem that has a long enough bolt, I'm sure you could either buy a bolt or do it with all thread.
The only complication I could think of is if the seat post inside diameter would allow the wedge to slip inside, in which case you just need somebody to weld a piece of metal onto the cut end. This might be necessary anyway if the wedge wants to bind against the edge of the seat post tubing, but if you get it really smooth this shouln't be a problem.