Print your own beefy construction set.
There’s a brand of industrial Erector Set called 80-20. It’s all based off of extruded aluminum beams with a specific T-slot on each face of the rectangular extrusion. Systems like the Shop-Bot and Lasersaur are based off that very mechanic. So, it stands to reason that some clever person would think to print their own, and Thingiverse user Luis has done just that. You can download and print your own here.