I use the CO2 method, it's not as hard to find dry ice as you may think, a lot of grocery stores carry it now, and sometimes you can get it at icecream places (Baskin Robins, Maggie Moo's, etc.)
Cervical dislocation may be the way to go for you though (if you dont want to whack)
I have never personally done it this way so PLEASE someone correct me if I'm discribing it wrong.
Take a screwdriver (flat head) or a firm metal ruler and press it to the base of the animals skull....then give a firm yank on the animals body. (This is how it was discribed to me, but like I said I have never done it so I'm not sure if that is the way to correctly do it, ask around.)