I would second what Missy said. I've only found one style of fitted (tabbed) diaper/briefs at any of the various grocery/department stores I've been in (Walmart, Walgreens, King Soopers, Safeway, etc.) and I've been told by the lovely people here, including Missy, that pullups are insufficent for bowel IC. After doing some research, I learned that the tabs are necessary because they allow for a more snug fit, which prevents any fecal leakage from falling out of the diaper. All that said, just find whatever you can in the way of tabbed diapers, and hope that you can order online soon. I'm bowel IC and I was recommended Northshore Airpremiums. I ordered them, but I have yet to try them out, so I can't attest to their effectiveness, but I know others here can.
I'm also given to understand that onesies and/or plastic/rubber diaper covers can help contain fecal leakage, because they increase the diaper's snugness (if that wasn't a word, it is now!)