Where have you seen that aluminum is fine?
The most common material is Steel EMT conduit. Unfortunately some brands are too soft. I had a set of rails wear out in a few hours of 3D printing, very minimal loading. I have tried everything I can get my hands on in the last year and a half.
You shouldn’t need a steel supplier, most countries have steel conduit, sold at a hardware store. Some don’t if you are in one of those countries there are lots of threads on specific suppliers, Australia seems to be the most difficult.