Where can I find these? I would really like to have a genuine Colt RO635 10.5" barrel, are they all gone now? I also heard that RRA made them, but all I see on their website is 16". Thanks!

Those barrels are out there, but mostly as parts kits or uppers from De-milled post sample 9mm SMG's.  Be prepared to pay a premium for that little dancing horsey.. Usually $850 new... You might try Bryan Pritchard in GA, he had a bunch of parts a while back.

Now for that kind of money, you can buy a bunch of RRA/ASA barrels, cut them to 10.5" and still not shoot them out in your lifetime.

They are hard to come by, but you do find them once in a blue moon. If you intend to shoot your SMG, I'd recomment you do as SBR7-11 recommends, buy an RRA and have it cut and rethreaded. You won't be able to tell the difference.

But if you're bent on having a Colt:

http://www.autoweapons.com/products/accessories.html