Troy, PRI, Midwest Industries, Magpul.
You may also consider either folding or fixed 45degree mount sights. Dueck Defense does A2 style fixed 45degree sights which are nice, Troy and Magpul (and others, I’m sure) do a nice 45degree folding set. Having them on the side allows you to immediately transition without removing the primary optic, and eliminates some of the fitting issues you might find with fitting folding rear sights under the eyebox of certain optics.