They mostly came from one dude in Japan who had a large cache of them. When he ran out they only became possible to find from other folks who had picked some up. They are available in the community but they are rather coveted by the people who have them. I've been looking for one for a long time.
Topre is hard to be in the market for. I can't find anything I want - Topre blank sets, interesting HiPro (104UK, 108UW) keyboards, etc. Very limited supply and it has all been sucked up. Topre themselves seem to have moved onto the R2 and RGB models. I'm always looking for this stuff if anyone has any extras - the most likely place to find these things is in this community.