I don't know if the information is online, but they do sell them. In fact, they'll sell you just about any upper you want. How about an AR in 45-70? 10mm?
Olympic Arms in WA makes carbine uppers in a variety of calibers. They use converted UZI magazines. I think that they're one of the bigger AR-clone manufacturers.
I have one of the oly arms 9mm conversions. They are fun and reliable. The only downside is it uses modified sten mags and they run $65 a piece. However you can buy a magazine adapter for $57 and use unmodified sten mags. I haven't had the opportunity to purchase one yet, but will in the near future.
Rock River Arms is working on one. If your not in a hurry it will be worth the wait. It will correct the problem's of the ones on the market now. Like no bolt hold open on the last round. Also will be using a better quality mag than the sten.