Heres a suggestion,
as your looking for a shell for a retro rally project i take it that a LHD shell would be OK.
Here in Spain their appears to be plenty of 4 door shells and i have seen the odd 2 door shell on the road and in scrap yards, good old scrap yards like we used to have in the UK.
Motor mania will transport a car from Spain to the UK for 550 pound's approx plus VAT, they transported my 131 to Spain last year (door step to door step) if you bear in mind that the Spanish dont use salt on the roads you will realise that even the most ancient of shell's are in pretty good condition, theirby saving a lot of replacement panels and welding.
So why not get a cheep (some times free) flight to Spain and have a look around a few scrap yards for the right car/shell, combined with a few days in the sun, could eventually save you a lot of money.
I live in Spain and if you were to find something in or around the Costas and or Granada region i would be more than willing to help in any logistical problems you may encounter.
Any one in Spain at any time drop me a line.
Now if you were looking for a Fiat (Seat) 500 - 600 i know where their are literally dozens of runners and some waiting for TLC, theirs even a 600 Abarth type for sale in Granada near wher i am for 3900 Euros (see photo on attached link)
http://www.sportingfiatsclub.com/forum/topic.asp?TOPIC_ID=2416Steve
PS: remeber they were badged SEAT's in Spain so if you do go around scrap yards its beter to have a picture of what you want in your hand.