What are you looking to spend? I have an upper with an 18" 5.56 White Oak Armory SS barrel with 1/7t. Somewhere between 300-400 rounds through it and has a JP 2 port brake on the end. It's not fluted though.
I have an upper I would sell, but it is not bottom or middle end. It is a top end upper, SS and shoots lights out. Mine is not fluted. If interested in knowing me, PM me your cell and I will text info and pictures.