It is a shame that it's so hard to find any "specialty" sizes in stores. It's also a shame that there aren't more fashionable options. I have found several etsy sellers that don't charge extra to make 3X sizes, for what that's worth (and the prices are reasonable!). Metamorphoza is one of them, there are several others I've found but can't remember the names. Of course, they tend toward asymmetric and such, so it might not solve the problem you just had.
Tim Gunn recently went on a rant about this, and I was like "GOOOOOOOOO Tim!!!!!" (link, if you haven't seen it)