Bortwein, who long ago contributed a lot of really great cover art, has a Threadless shop with lots of cool t-shirts (and posters and skateboard decks!), and they've been on sale this past weekend and will continue to be on sale another 48-ish hours.
https://bortwein.threadless.com/
You can browse his old cover art here:
https://www.sfjukebox.org/fights/galler ... e=bortwein