ive got a saito/cusco 7 point bolt in, in my track car. picked up from a jap wrecker. seems to be a pretty well built cage. dont see to many pop up though. may be worth trying to source one from japan?
http://www.rhdjapan.com/cusco-safety-21-roll-cage-7-point-full-capacity-through-dash-skyline-r32-61817