I hear tyres off mopeds are particularly hardwearing. Maybe replace with some of them?
George is right, that's probably your best bet.
These are good.
http://cgi.ebay.co.uk/HONDA-SUZUKI-KAWASAKI-YAMAHA-TRACK-DAY-TYRES-DUNLOP_W0QQitemZ220348622186QQcmdZViewItemQQptZUK_Motorcycle_Parts?hash=item220348622186&_trksid=p3286.c0.m14&_trkparms=72%3A1689%7C66%3A2%7C65%3A12%7C39%3A1%7C240%3A1318#ebayphotohosting
@sorethroat started
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George is right, that's probably your best bet.
These are good.
http://cgi.ebay.co.uk/HONDA-SUZUKI-KAWASAKI-YAMAHA-TRACK-DAY-TYRES-DUNLOP_W0QQitemZ220348622186QQcmdZViewItemQQptZUK_Motorcycle_Parts?hash=item220348622186&_trksid=p3286.c0.m14&_trkparms=72%3A1689%7C66%3A2%7C65%3A12%7C39%3A1%7C240%3A1318#ebayphotohosting