That was my thinking, too. I liked the standard CE2 cartos, but they didn't hold enough juice. The XL cartos I got wouldn't wick for anything. I tried pulling the silicone rings up, I tried making the side holes (where the wick passes through) a little bigger, I tried thinner juice and thicker juice. They all either stayed non-wicking, or they leaked. I threw up my hands and got a MAP tank, and now they're all going to be reborn as guts for my tank.
The only place I know of to get the tank is COV. I contacted the manufacturer and he said he's got a very large ordering headed out, so get your name on the notification list if it isn't already.
And I think you'll love your ProVari. It's everything I wanted in a PV, and a few things I hadn't even thought of. It's been glued to my hand since I bought it.