The best site (in my opinion) for second hand microlights would be
AFORS.
If you want data sheets on types, then most UK microlight types have downloadable data sheets from the
BMAA website (under TADS and HADS) or the
LAA website. The choice is enormous, and almost invariably, whatever the type, somebody on PPrune will have flown it and be able to offer a useful opinion as well.
G