I think there are three different types of connections for an IBC. One is a
really coarse thread (top two images below), one is a standard NPT plumbing thread and the third is a deceptive one. It's a really fine thread on the end of the fitting. But it's really only there to screw on a dust cap. The actual connection is a cam lock recess behind the small threaded bit (center and lower two images in this picture:
If you actually have the cam lock, don't worry about the ruined threads and go get a cam-lock connector to latch onto that puppy.
If you have the NPT style (standard plumbing thread), I'd try the file trick Gary suggests. If that fails and you really need it to work, I'd get a galvanized metal fitting of the same size (perhaps a coupling), cut it in half and use the piece as a threading die to smooth out the grooves of the threads. It's hard to describe and I've never done it but I think it would be worth trying. I can make up more words to try to describe my crazy idea if you want.
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