Maybe you can buy reproduction wheelhouses for a tri-five Chevy and use them as patch panels for yours. The only other thing that I can suggest is find a donor car and start cutting.
There's an NOS p***enger side wheelhouse on fleecebay right now. I doubt you want to pay $400 plus another $100 for shipping.
If it's just going to be a driver, I think I'd go cut some out of a late(r) model donor and make them fit.
Thanks everyone , just making sure I didn't miss a supplier. rear outers our off now, so now is the time to get it done.