I know 21st century fireamrs had some colt commando SBR's but I'm unsure of prices. As phylo mentioned get with Corey he can prob get you anything that's available.
Corey was able to get me a 10.5 noveske factory SBR that is such the ****. He also procured me a 1 time only custom 300blk 8.2" upper with all the sexy accoutrements. I still have yet to post pictures of it. He was able to do this when it was impossible to find one and i searched for a year. He has a direct line or something. I'd send him a PM on here as tracking him down at BGF is kinda hard with them working on the indoor range and all. I went there yesterday and he was off getting wood or something. You could also just wait until all the fuss is over, but i'd hurry. As with any gun purchase, it's better to buy now than wait for the price to go up.
I picked up a Colt 6921 a few months ago via a dealer in Arizona. I guess I paid a bit of a premium for it was the one I was looking for. The are most definitely out there but you may have to look around for what you want.