The top online and mobile sportsbooks in Colorado allow all kinds of MMA betting. That means they post odds for various events beyond the UFC. This includes Bellator fights and any others coming from reputable fight companies who provide fight data that can be trusted.
Bellator is second behind UFC in terms of UFC MMA interest, but finding betting action isn’t quite as easy. It really depends on the book. If you click on the MMA section at legal sportsbooks, you’ll see a listing of all upcoming fights for which they are taking action.