Is there a definitive database somewhere of which ones do?
What I found in the past is that some airport directories / flight planning progs show "avgas" but it is not for sale to visitors.
Peter, I am afraid that, as long as you try squeeze Italy into things like databases, you will not organise a successful trip there. It just doesn't work that way, as little as you can force toothpaste back into the tube.
Regarding fuel in Italy, if you are planning a trip just send me an email and I will enquire.
I have a strong suspicion that quite a few Italian facilities refusing to sell avgas to foreigners paying with cards will gladly sell it for cash.
I am sure there is no problem at airports where there is a handling agent, or where handling is mandatory. You just phone up the handler, in English, and he must speak English because he is a business.
It's the ones lower down the scale. From my limited experience of trying to communicate with those, I am sure Italian would be required.
I have a strong suspicion that quite a few Italian facilities refusing to sell avgas to foreigners paying with cards will gladly sell it for cash.
I am sure the Italian pilots here can confirm, but my understanding (from Italian pilots) is that Italian clubs work under some sort of tax concession which prohibits fuel sales to visitors.
The way to deal with that is for a club member to fill up "his" plane 
But obviously you are not going to get help like that unless you can speak properly, and give a reasonable reassurance that you will keep your mouth shut afterwards. This is the same situation in other countries where parking availability may depend on "extra payments" - a foreigner is simply not going to get that.
Peter, I am afraid that, as long as you try squeeze Italy into things like databases, you will not organise a successful trip there. It just doesn't work that way, as little as you can force toothpaste back into the tube.
Having lived and worked in Italy, all I can say is - Jan has it.
