At APA in South Denver there is Mayo Aviation (probably the best 135 on the field) International Jet (pay is not too good, and you are on call, must be within 1 hr.) there is or was another operator on the north side of the field, In the 1st big brown hangar. They flew lears, mostly air ambulance if I remember correctly. You could also try Jeffco (BJC) or maybe Front Range (FTG) but Centennial (APA) will definately be your best bet.