There are Augustinian nuns at the church of Quattro Martiri Coronati (Four Holy Crowned Martyrs). Across the hallway, also, at least last year, there were sisters of a new Congregation, the Little Sisters of the Lamb, with a habit like the Dominican but in blue, with tie-on kerchiefs for veils.
There are also Dominican nuns somewhere near the city--I don't remember where, but if you go to Santa Maria sopra Minerva (walk past the left side of the Pantheon and it'll be the big flat facade on your left), I know they probably have the address posted.
Then there are the active Suore Francescane dell'Immacolata--Franciscan Sisters of the Immaculate. Here is the address:
Suore Francescane dell'Immacolata
Via G. Zanardelli 16
Roma 00186
It's walking distance from St. Peter's, down along the Tiber basically and then across. It's inside an apartment building, I guess they transformed a flat into a little convent. They will give you lunch if they're there

Maybe

At least, if you tell them you are there for a vocation.
I'll PM you the telephone number, seems it's best to call first as they are often out and about & there's only 5 or 6 of them there.
*edited to add the FSI