It turns out that the geometry behind fair dice is more interesting and complex than you might first guess.
Professor Persi Diaconis discusses all kinds of interesting properties of fair dice as well as his interesting paper on the topic.
Getting fair dice for any number is very hard, if not impossible. But it turns out level-up dice have a unique ‘unicorn dice’ that you change the end cap and then roll in a circle. They’re pretty overpriced at $110 for a whole set – when a regular set will cost you $5, but a dice in this configuration can get you a fair roll for any value range.