Trials scene pretty much sucks in York... Good job I just got back to Liverpool, 3rd year at uni starting now! There are some good places in York though, check out that Yorkbiketrials website, never met the guys on it but they are good riders!
Good places to go are near Cliffords tower and the Crown Court, a little are covered with walls and benches by Argos by the river, Clifton Moor has miles of rocks lined up by the sides of the road... The centre is always to busy to go riding unless you go so early in the morning or night. Ill give you a shout sometime when I'm back!
Cheers