edward, there are no "problems" merely "challenges" ;-) My assumption would be that the TI ones would be the ones with the highest demand. The 4-door ones are sometimes available on E-Bay Italy/UK/Germany or even at alfasudparts.co.uk as NOS or fair used ones, for the TI cards nothing is available.
It should be looked into in more detail regarding the 1st and 2nd series differences. I suppose the mould is the same, just the fabric and trim are different for these series?
One advantage of the TI ones is that as far as I know they only came in black. For other vehicles like the Giardinetta for example (which uses TI dimensioned cards) all 4 colours were available, black, red, tan and blue.