Who makes lowers that are registered as pistols?  I want to buy just the complete lower, so if you know where I can order one, please share!

I haven't been convinced that a stripped lower can be registered afterwards as a pistol, every FFL dealer I talk to says it's illegal (not that I trust what they say completely, but they are the ones who would then mark the lower in their book as a pistol.)  

If I'm wrong on this, please share the specifics so I can share it with my FFL dealer.

Just about any dealer should be able to provide you with one.  Try Dennys or CMMG.  You could just buy the stripped lower (transfered as a pistol) and install the Lower parts kit, and buffer assembly.  It is pretty easy, and may save you a few bucks if you find the right dealer.  If you find a local dealer that has them in stock (all the parts) you should be able to get a decent price.  Or buy the Lower from a local dealer to avoid transfer fess (30 -$35.00), and then get the rest on line.

How do you buy a stripped receiver "transferred as a pistol?"  Does that just mean the 4473 form is marked "pistol," or does it have to be transferred from the manufacturer to the dealer as a pistol?

LAR Manufacturing (Grizzly) actually sells lowers marked as PISTOL.  I have a few.  :)

Quoted: How do you buy a stripped receiver "transferred as a pistol?"  Does that just mean the 4473 form is marked "pistol," or does it have to be transferred from the manufacturer to the dealer as a pistol?

Distributed stripped lowers (never been built into anything yet) are able to be sold by the dealer (FFL holder) as a pistol or rifle lower. Just tell them that you want to use it as a pistol and they will do the appropriate paperwork. Then you have a pistol lower.