Sorry. You can’t block this without blocking all 3-d printing. Furthermore, if you try to block the CAD files, they’ll just be put on an offshore server.
It's already on PirateBay.
They already are off shore: Defense Distributed’s downloads are on Mega, Kim Dotcom’s new file sharing site.
What’s more, if FReepers attend to my advice, the CAD files with exist on thousands of computers here in the U.S.: everyone, even if you don’t expect to be able to afford a 3D printer in the next decade, even if you don’t want firearms in your house for whatever reason, download the files — do it on public wi-fi, encrypt the results under an obscure name, and delete the originals using military grade deletion if you’re worried the Feds will know you have a copy.