I found some great transfers (“decals” in American English) on the web and ordered this one. It’s a Canon 5D Mk II Mode Dial and it’s really easy to apply. It also comes off cleanly if you change your mind.
The decals come from Suzie Automatics and are listed on Etsy.com. The iPad ones are the same size as the MacBook/MacBook Pro versions as far as I can see. This one cost US$15 with $3 shipping and it arrived about four days after ordering.