Follow the link QinteQ put on his reply #4, and in short sadly it is probably going to cost you some money to actually do it - good AUTO locksmith and second hand remote and you should be good to go.
I'd have thought if you advertised it on the Fiat Coupe forum and poss Carsandclassic.co.uk it would go quite quickly given it's history and condition. There's always a few for sale, but non quite as nice as yours!