Bernhard,
There are quite a lot of lenses available on the after-market, but I also don't think that Pentax actually formally discontinued 645AF lens production. The film system remained surprisingly popular in Japan, even if it faded here. My guess is that re-starting production would be relatively easy for Pentax, since it is such a large and well established producer.
Pentax has been very clear that the 'old' lenses work just fine on the 645D, and there will be more of those than bodies for a long time. Buy a 45-85 and wait for a body :-)
That said, some the the lenses were always rare, such as the 100-300 and 33-55. I have both ( :Phe ) after years of trolling ebay, but I expect to see new glass in short order.
- N.
ps. and yes, these questions will be asked when Pentax starts talking to westerners about the camera. Pentax Canada has been very helpful to me, but I get the sense that the Mothercorp wants to get the launch done in Japan before opening a multi-front campaign. Can't say I blame them. But she's coming, and soon.