Am I the last person on the planet to have heard about these? And what a brill idea! Hollywood Lights does self-adhesive lampshades in a bunch of different sizes and shapes and you can even create your own custom size. Slick.
I'm thinking maybe a vintage map or fabric or maybe some ribbons or handmade paper or... you get the idea.
Find them here, and don't be put off by the acres of froof in the picture, they do some nice clean-lined stuff too.