I visit two dealership by my job in the OC and they both only had Twos and One model Three I know a few of the larger dealers around have a few Four
Now that the incredibly badly named Prius v is out, you will only confuse people using roman numerals for trim levels or generations.
Jimbo, that's why with 2011, they technically renamed them as Four and Five. But... once you start it one way, it's hard to shift the masses. I've edited the thread to reflect the new naming (Four and Five vs. IV and V).
I was at Piercy Toyota today in Milpitas (NorCal) and they said they will be getting a Prius Five in the next 2 or 3 weeks.