Although it now looks like you can but directly from Superior. Check Qtec as well as the other big distributors as well.
just a heads-up
couple of months ago when i ordered my 10 bolt carrier shims from them their order page where you enter the credit card number was not secured (not https / SSL) but plain http clear text, i used a gift card to place the order (the card had $25 on it and the order was $20) - so pay attention to that. I wrote them an email about it, didn't check if they fixed it or not (at the time I also tried to put https in front of the address but didn't work at all, luckily i had that gift card handy otherwise i wouldn't have send my CC number unencrypted over the internet).