@ Hans
At the moment there are several 2.5/105mm's offered on Marktplaats
There's an Nikkormat FtN for sale with a 28, 50 and 2.5/105mm for sale, considering the body mentioned very likely to be pre A-i lenses
Similarly there is a 2.5/105mm (not clear whether it's the Gauss or Sonnar version) for sale since May 7th no one apparently has made a bid on yet
There's also a 1.8/105mm for sale, but that version does not have the near mythical reputation of the 2.5
There also a a pre AI 2.5/105 for sale (for Eur 90 !!) at a classical camera store in Rotterdam, but the seller himself mentions it shows signs of regular use

That said, I personally never liked the 2.5/105mm I bought in the late 70's together with my F2AS (I think it was a Gauss version).
Probably my fault, as I primarily used it as a low light short tele, usually wide open with shutterspeeds of around 1/60th
Which as a rule resulted in blurry images due to camera shake, and after a while I traded it in for a 2/85mm Ais.
Not a brilliant performer, but a good/practical workhorse lens for the low light shooting I used it for
There also are several 24mm's for sale, even a 2.8/24mm Ais for Eur 129, but they all appear to be more modern (not preAi or N-C) versions and might not be what you're looking for
HTH