PSA is really weird about what they'll ship to MD unless an FFL with an account orders it- then they'll ship anything.
ETA- As stated above, they will ship stripped lowers to your FFL, but not completed lowers or complete AR's. An FFL with a PSA account has to order them.
That's a good point.
Now that I think about it, all of the FFL's were on PSA's preferred list. I consider that a "best practice" when ordering off of any firearms website (to stick to their preferred dealer list).