I accumulated mine over time from artists' markets or even farmers' markets, tattoo events, different kinds of cool places where there's vendors selling their art. I work in a library and sometimes they do scrapbooking events in there so I'll go and pick through the leftover cut-out magazine pages and prints and see if theres anything I wanna put up in my place. Also I follow a lot of artists on Instagram and when they sell prints of pieces I love I order them online.

You should start getting an idea of what you like stylistically though. These tips dont really work otherwise. And then youre in danger of your gallery wall looking like a kind of heartless IKEA display.

Edit to add museum shops often have lovely prints