Are you looking for a quad rail?
For a good inexpensive quad rail look into the Troy Industries 13" Bravo Battle Rail
Personally, if I were shopping for one right now, I'd get a Daniel Defense MFR
I don't measure a man's success by how high he climbs but how high he bounces when he hits bottom.
George S. Patton
It is impossible to defeat an ignorant man in argument.
William G. McAdoo