Last time I was in Florence I had a heck of a time finding anything. You're much better off in Rome, but even there your choices are limited, there are only a couple of places that have anything, their hours are difficult and it's expensive. I'll drop an inquiry on the Italian thread that was going around a few months ago to see if anything stirs up.
"There is a time and place for all things, the difficulty is to use them only in their proper time and places." -- Robert Henri
It's been close on a decade since I was in Firenze, so take this for what it's worth, but there was a camera shop with Hassys, Rolleis and Leicas in the window within a few blocks of the Bargello museum.
Hi Jim, I live in Florence and I usually have to buy film online...
Unfortunately the shop mentioned by "TheFlyingCamera" doesn't exist any longer...
BUT, only to limit myself to the central part of the city, you can find 120 films - BW and color - by BONGI, in Por Santa Maria, the road that leads to the Ponte Vecchio (here you can find a map)..
Hope this helps and enjoy these coooold days in Florence!
if you will visit only the historic center, Bongi is probably the best choice, together with Fontani (Viale Strozzi 18, just in front of the Fortezza Da Basso).
There are some larger photo shops in the suburbs, if you're interested I can give you more details.
I hope you'll enjoy your visit in Florence.