You mean Venice? I think you will be too busy with your girlfriend to toy about diving gear when you'll be there. That place has the mysterious, magic power of boosting people's erotic potential. Last time I took a holiday in Venice with a girl, I remember we spent all the time making love 7 to 10 times a day. That was insane. I was very thin and pale when we got back home. But happy.
However, your question has been asked recently on deeperblue, and I told the guy that from information I had form venetian spearos, there is no good dive gear shop in the historical center, but a good one in Mestre, which is the firm land district of Venice. It's called Mestre Sport.
http://forums.deeperblue.net/general...ghlight=venice