High power rifle source

I'm thinking of putting together an upper for my RRA NM AR-15. I'd like to go to a flat top and at least a 24" barrel with an extension. My rifle is fine for service rifle matches, but the guys with the pure high power rifles have an advantage with better sights and a longer sighting distance. I need websites that have uppers and sights. I know of Champion's, but thats all. TIA...Joe

joe