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Have you checked with Spike’s Tactical?
He makes pistol marked lowers.
I actually just put together a 9mm AR pistol with one today. 
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The website is at http://spikestactical.com/catalog/index.php
Here is a direct link to the lower http://spikestactical.com/catalog/product_info.php?products_id=51
It’s a normal AR lower marked with a pistol designation. As it comes it is ready for 5.56/.223.
In my case I added a magazine block that adapts it for 9mm mags.
If you don’t see what you want just contact them. They will assemble the lower parts kit and a stock to the stripped lower if you so wish.
You will usually get in touch with Angela, and she will take good care of you.
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Heres some bad news on RRA lowers. I’m an FFL and normally order about 10 RRA lowers every six months. I stash them and wait till someone wants a Rock lower, then I have them stocked. I ordered 10 rifle and 2 pistol lowers over four months ago. They then told me 6-8 months. I’ve been using other brands while I wait. Only saving grace was after I hung up on RRA from my hartbreak, Armalite just got a bunch in. Good luck finding a RRA. If you find them cheap let us all know. Later
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Why bother with a pistol lower? You can use a normal lower as long as it’s marked as a pistol when transferred to you.
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Understood. I just picked up a stripped lower for a pistol. Made REAL sure the 4473 was done right. Had my guy fill it out with me watching so we were all sure.
Hassle…huh?
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Anvil Arms has stripped pistol lowers on sale for $100.00 and they are marked REGISTERED PISTOL on the right side of the lower.
I have an Anvil Arms lower on the way. They are real nice folks to deal with.
Wow , my local FFL has a freakin pile of RRA lowers that can be registered as a pistol when he does the paperwork
It doesn’t have to be marked as a pistol lower, unless you’re dealing with some goofy state law. It doesn’t have to be on the 4473 as a pistol, either.
ATF says in the letters I have seen that you must establish that the lower has never been used to make a rifle. The recommended method for doing that (again, acording to ATF letters) is by getting a letter from the manufacturer.
Many people find it prudent to indicate on the 4473 that it is a stripped receiver, as opposed to an assembled weapon.
Sent in my money order today of one too.
CMMG has good availability and are nice people to deal with.