There are probably better forums to use but plenty of 10m pistols are bought and sold on here. I think you just need to pick a price you would be comfortable with. You might get a bite on here. I've found a lot of kit like that (pistols inc) gets sold within clubs. People invariably know the seller and or, they and the rifle/pistol can be vouched for by other members if its being sold to someone new.
I've just shot my 10m round for Feb this afternoon with my Anschutz 2002 SSP. I'd have a 10m Challenge if I could as I have a Challenge HFT for FT and a Steyr Evo10E for my 10m pistol.
Unfortunately I'm just not flush
Steyr Challenge HFT - HW97K - BSA Mercury Challenger - Anschutz 9015 One - AA Pro Target - AA Pro Elite - ASI Paratrooper (R) - Walther LP500