hello mate,
1. to reattach it: just get some of that leatherette fabrci and cut a thick enough stip to go over the seat cover underneath on the base and then use a staple gun to hold it back in place.
2. to recover: there are quite a few places that recover seats - look in the back of the MCN (should be quite a few)
3. for a replacement: ebay has seat come up quite often
HTH :thumbup