I've found some unique comic book shirts on TeePublic.

The quality has been good so far.

They also have the option for the customer to select different background colors for the shirts which is a nice feature.

I guess the only disappointment I have is the following shirt is no longer available.

They should probably keep all their designs on file forever and print the shirts on demand.

Vintage Retro Bronze Age Avengers Cover
Thanos Endgame
sold by Osprey