if the serial number in on a sticker on the radio (it should be unless its been removed) you can use the serial in a code generator to get the code. i dont have the code generator for these models (because i couldnt find it) but i'm reliably informed that it is available. i dont know if fiat can do it, or if they would be willing unless you could prove ownership.
you need the CD changer that is fitted as standard. the Grundig 6 disk type. it uses the 13 pin round terminal cable. it was fitted to other cars as well (seat iirc).