eBay is your best bet. Most parts will come straight from China, and could take 10-12 days for shipment.
Sim Card Back Door Case Cover For HTC At&t iNspire 4G | eBay
WOW! They want $26 for that thing?
Call HTC. That's what I did. Got the number from their website. I asked for a replacement sim cover and a battery cover just for the hell of it. They sent me both for free, even shipping. Just tell them it won't sit right on the phone somehow. Had it at my door in 3 days. Again, this was no cost to me, whatsoever.
Wow, OK, thanks! I'll give HTC a call, hope they're as helpful for me. And thanks for the ebay link.
@potnug52 I was wondering if you ever got around to calling HTC. What did they tell you? Thought others might find it useful to know your experience with them on the matter.