Frewer can be persuaded to do batches of old shells, but you do need to buy a few to make postage reasonable. Had a batch of Metro 6R4s we got pulled from him, got one spare left.
Horizon Hobby UK got Parma to do a batch of
Escort Cosworths for them due to a few requests a few years ago, should still be available from them.
PK Racing still have a few old shells listed, including the XR3, but they seem to have removed the English version of their site.