Federal law requires that handguns can only be bought in your state of residence (though you can buy a handgun and have it shipped to an FFL in your state, and have the FFL transfer it to you).  Long guns can be bought in any state.

However, Federal law also requires that the laws of both states be followed.  Since the PRK requires that all guns have a DROS (Dealer Record Of Sale) be run by a PRK FFL, PRK residents cannot buy guns out of state at all.  And a PRK FFL cannot transfer guns that aren't legal in the PRK.

-Troy