I know the area as I've been in a few groups at these fields. The best way is to become "known" and let it be known that you are looking for a share in an aeroplane... most shares aren't advertised. Try chatting to the instructors when they're not busy, they often have an ear to the ground... good luck, I hope you find something suitable.
PS... don't leap in too quick... joining a syndicate is like getting married!
PPS... People join and leave groups so the Pup might have a share or someone thinking of selling... no harm in asking. I think every pilot at Gamston has had a share in NS at some time (me included)!