I got nothing.....but Shawn Carlock @ defensive edge does.
For my less than custom rigs
I make my own levels. Grind the bottom of a scope ring that has enough meat with a dremel tool. Drill to hold a bubble level out of a cheap plastic level. Devcon/jb weld it in and there ya go.
I got a "decent" looking one from 3rd Generation shooting supply for a rig that I didn't want "my touch" to be apparent.