[bluefish81]

Typically you can find Mascarpone in tubs. In the grocery stores here, it located near most of the other soft cheeses like bries, foreign cheeses and things like that.
Otherwise, if your city has an Italian grocery store, they will carry it.
I also have a really good tiramisu recipe, using mascarpone that I'd be happy to PM you. It's not too hard to make and I generally make that ahead of time.
That Limoncello idea of RedRoseSAI's also sounds excellent.