It might be worth having a word with Terry Briggs at a rallycross meeting - the rumour of how he built his spaceframe Audi TT bodywork was to borrow one for a weekend test drive, cover the thing in clingfilm and then cover it in fibreglass - hey presto one mould. I have no idea how true that is but he should at least be able to give you a few pointers
I assume you've got the original metal panels so something similar could be possible for the celica?
Failing that John Cross' Xsport should be able to make the parts (although that'll probably be ££££££££)