Yup, viral content and events are great for 'commemorative' swag, and there's plenty of companies that offer print-on-demand for things like that.

One time I experienced a "trending topic" first (or second)hand; the app we were building accidentally sent a pair of test notifications to 2-3 million people, first the test message, then a second saying "zodat Hajo het ook gelooft" (so that Hajo (name) believes it too). That took the daytime internet by storm; news articles, radio segments, twitter trending topic, etc.

I mainly followed the topic on Twitter, and before long there were adverts on there selling swag related to the trending topic. There's companies (or even bots?) scanning Twitter, making swag-on-demand for trending topics.

And sell what exactly? It’s not like he owns the copyright on the maritime map or on photographs of the ever given.

Commission some basic art about it?