We are not allowed to buy sell parts here at the Colt forum, all that are done at the Equipment Exchange, but we could let you know where to find them.
Colt detachable carry handles are the same for carbines and rifles, the recent ones up to about 5 years back (or even more) have a square symbol forge mark which are forged by Brass Aluminum Forging Enterprises.
I've seen some on Gunbroker.com, just search for "Colt carry handle" and look for the square forge symbol markings, other places to frequently check is the AR15.com Equipment Exchange, also try other classified sites like ArmsList.com, sturmgewehr.com, etc.
If you're really out of luck finding a new one your last chance would be to look at SpecializedArmament.com but they're very expensive there about $175.
Good luck.