My son recently purchased (privately) a 156. It came with 2 red keys like the one here:
Alarm Box, Radio Receiver And Key Fobs - Alfa Romeo 145 - 146 Forum
except that neither has the black rubber? on the side - ie the pcb's are both exposed & neither remote works.
A fortnight after purchase he had to replace a pump in the Selespeed which certainly didn't help his bank balance so he's not game to ask the dealer about the remotes.
The local locksmith advised me to search for "key blanks" or "shells" on the net but so far I've been unable to find them.
He placed one key in his machine & suggested that with a new shell he could transfer the innards & have it working again.
btw, we're in Queensland, Australia - home of "the best job in the world"