The word on the street is DESPP is refusing to transfer anything other than complete firearms. In other words they won't even allow the transfer of a 1911 frame.
That is false. They can not refuse. Its not their option All they do is give an approval of the person, not the firearm. If the NiCS check comes back clean, they approve. Period. When I call into the nice ladies, I tell them if the person is a CT PP holder and if the firearm is a "handgun or non handgun". But I never specify if it was a frame or a long gun. I've only had a couple of waits. In one case I got an approval the next day. In another case, I heard nothing after 3 days. I did the transfer without an approval in full compliance with the law as well as my own sense of ethics because I knew the person.
So to the OP, here are a couple of things.
1) It is perfectly legal for you to buy an AR lower receiver IN CT. It is no different than a Remington 1100 receiver. Both of them are merely receivers. Both of them can be built into fully compliant firearms or illegal AWs. It is up to the buyer to comply with the law in how they build up their receiver.
2) Stag is currently making and selling a CT compliant .22 LR AR15 that uses standard AR15 uppers, lowers, and I believe barrels.
3) I was an FFL in CT until this summer. If I was still a FFL, I'd gladly sell you a lower. Its perfectly legal to buy, sell, or possess. You just can not build it into an AW.
Regarding your last question about registration. No you do not "register" normal firearms in CT. They track transfers via DPS3 forms. That is in effect the registration. Prior to PA13-3 you could purchase long guns like an AR from non-licensees and no paperwork was required. You gave the guy money, he gave you the gun. In that case, the state would never know that you own the firearm. No registration would have ever been required, unless one of those privately acquired firearms was deemed an assault weapon by PA 13-3. In which case you would have had to have registered it by 12/13/13
Don
p.s. PM me. I can probably find you a dealer that will transfer you a lower. Again, there is nothing even grey about this. Its simply a receiver that can be built into a fully legal firearm (single shot .50 cal bolt action) or an illegal AW.