M_Fix There's ACI Space but I'm not sure if it works with non-italians. And you can't only look up too many plates or they block your account.
Since 2 years I'm checking plates of old cars I spot (even if I rarely publish them here, but I photograph many of them) and they never blocked my account; just don't look for more than a dozen a day and there is no problem. But yes, I think that non-italian people can't use it, because SPID is required to login (for non-Italians who probably don't know what SPID it is: it is a kind of digital identity that is necessary to use the online services of the public administration).
Yes, I know, but it doesn't always work. It's because the public registry is managed by ACI, and they aren't so much keen to give info to third party apps.