On our bravo the Blue key had a worn blade.
I bought a pattern key from ebay, then got the blade cut.
After that I cut the old key open and removed the chip, then inserted it into the new key.
It worked a treat.
Pattern keys from ebay do not contain a code in the chip they contain BTW, so you cannot just program them to the immobiliser. They need to be pre programmed with a code by a locksmith. The other solution is to get a secondhand old key from another Fiat (or an Alfa) and swap the chip over as the old one will already have a code inside it. Then you can program the immobiliser to recognise the new key with the red key.
The way locksmiths clone keys is to read the code in the existing/old key then program the new key with the same code.