Poison spyder is the only other commercial manufacturer of commercial sold roll cages, but if you call around, allot of independent off-road shops have contacts with locals that build and install roll cages.
Personally I went with Rock hard 4x4 for mine since there cage bolted to the existing cage with no damage to the interior and it had the option of tyeing into the frame, and that is where any roll cage will gets its strength and safety factor.
Here in Utah I found the cost of having one designed and installed was comparable to buying one off the shelf.