Several AR pistols on the MD approved handgun roster. Probably tough to find one in stock, though I did see a Sig in stock at Freestate a couple months ago.
The PLR and Sig 556 pistols aren't really "AR" pistols. Though fun to shoot anyway.
Plenty of threads on here on how to legally buy a lower and build a pistol for personal use.
Several things to be careful of such as items that would make it an AOW or pitfalls of owning what you could turn into a SBR.
Yes after completing the ATF paperwork and tax stamp. Do not have an available buttstock handy before that or you could be charged with constructive intent. (A big no no)