Just like there's no law against shipping ammo into Mass., either, but Marsha sends cease and desist letters to anyone who does and who comes to her attention, so most online vendors won't do it.
Really, if the powers that be were solely interested in making sure that only eligible people received ammo, they'd work out a deal with the online vendors where the vendor keeps a photocopy of your LTC/FID on file, but that's not what they're interested in. They just want to make it as much of a PITA as possible on those of us who (1) comply with the law and (2) want to save a few bucks. *fume*