Light helicopters make do with one bottle. I have an R44 and EC120 with pop-out floats and both use 1 bottle.
I think that you can get an idea of how many R44 have floats from the registration details. I believe that only the Clipper model is floated (from the factory). I think that DART make an after-market emergency pop-out float kit for R44 (and R66, and other makes) but I don't know how common such after-market kits are. Others may know different. Looking at R44 Clipper models as a percentage of total R44 registrations will therefore undershoot the fraction of floated machines but it will give you a "more than or equal" figure.