All credit to you, but this BBS is probably the best place to buy and sell air rifles amongst genuine enthusiasts. The For sale section may not be categorised, but it works.
The best thing about this place is the sense of community - unlike say Guntrader, which has to be the biggest shotgun classified site, but it is just ads, you know nothing about the people selling. Personally, I like buying guns here, because this place really is a group of friends passing the time of day and occasionally trading stuff.
Just my thoughts FWIW.