I have seen a lot of these knives I like, but they never seem to be available anywhere. Do they just make limited runs of each model to keep them rare for the collectors or what?
They generally make one model at a time, then never make that specific knife ever again as a general production model, but you can still order them from the custom shop (about $100 per inch,) or they might offer them at knife shows, etc.
So generally about the only way to get an old model fast is to buy one on the secondary market, and most, if not all, end up selling for more than they originally were. Occaionally you can find a nice used one at a good price though.
www.bladeforums.com is a good place to buy them. Give or take 10-15 per day go through there.
Busse is taking orders for a lightened version of the Team Gemini on their website right now. The ASH-1 is a little harder to find, but a post in the "want to buy" section of Bladeforums should turn one up for you.