CRE (track) is not far from you in Calhan CO, The Track at Centennial is on the south side of Denver, IMI is just north of Denver, and as Stacey Cook mentioned, Grand Junction Motor Speedway is (a bit) west of Denver. There is also a track at Bandimere speedway. You can run a shifter at any of them.
Check out club racing at all of the tracks in the spring. I don’t want to influence your decision as you should choose the class and track that appeals to you. There are some VERY good shifter drivers from this area and you’ll see them using the local races as practice for the big nationals. Stick with stock moto for local competition and then you will have a package that will be legal for racing in other series.
Do you have a budget in mind? Are you planning on doing a local series or just occasional practice days?