try in some facebook groups, cinquecento and seicento owners really like them valver engines and i'm sure someone will have one tucked away...
If you really really cant find one anywhere you could use a later one, you'd need a adapter plate so the throttle body will bolt up but its doable if you really can't find an early style. It will just bolt up to the head fine.. to valver swap a cinq/sei most people use the later engine as theres loads of them about whereas the early 1.2 is getting thin on the ground - and then you bolt all the early parts to it, so inlets are interchangeable