Looking for a source of used 15" slicks

a friend has an MK GT(x) - can't remember whether it's a 1 or an R and needs some slicks for it. He will be running it in the modified category of speed events up here and needs some slicks.

Any pointers anyone ? Finding used 13" slicks doesn't seem to be any sort of problem, but 15" is a different matter.

P.S. Out of interest, it's running a 2.0 zetec on Weber 45s and alpha ignition.
Audi transaxle as well. Photos later perhaps. We may be going for a bit of a secret testing session later.
Not so secret now :-)

Renault Clio cup use 15" slicks. 190/580 15.

Adam