People have built their mining rigs, fortunately the video card market has dried up and hashrate growth should come to a halt.
Even though the best video cards are not freely available in the US, they can be obtained in other parts of the world.
It's likely that the vast majority of previously sold Radeon 5XXX and 6XXX cards are *not* currently used for bitcoin mining. Therefore, I think a larger source of new miners are existing Radeon 5XXX and 6XXX gaming enthusiasts who can easily install mining software on their otherwise idle game computers.