Terasic still sells them. The price is much worse than when MiSTer was taking off, but my gut feeling is the project's picked up enough inertia that it doesn't matter. See: https://www.terasic.com.tw/cgi-bin/page/archive.pl?Language=...

Kit-sellers like Misteraddons also get them back in stock regularly. Reviews on their site suggest they shipped out a batch last month.