What do you mean? The police shut down 3d gun factories every now and then, and here's a EP briefing about it https://www.europarl.europa.eu/RegData/etudes/BRIE/2025/7758...

That seems like the way to go about it. Address when people are _selling_ guns. The fact that they were printed and not imported from Yugoslavia in 1990 doesn't really matter. Trying to stop people with 3D printers (Or metal tubes) from creating guns seems almost impossible.