I'm pretty sure Neptune in Boulder rents them. Its off south Broadway next to the Southern Sun Brewery. Alpenglow or the Bentgate in golden might rent em too. Bentgate is near Woody's Pizza in the downtown/touristy part of golden (the one with the big sign going over the road). Alpenglow is up off Highway six in a little strip mall right before the entrance onto C470. Look em up. Alpine/Mountain Quest Sports carries them as well, but they are up in the Mountains west of Vail in Edwards.
I think EMS in Boulder is going out of business. Everything is 30% off or something, I'm not sure what is left, but they would probably be selling the ones they used to rent if you want to buy one cheap.