Lots of guys make steel ones, just need left and right hand taps and the appropriate tubing. 1 1/4" tube with a 1/4" wall gives a 3/4" ID that a 7/8" tap will cut threads into, that's what a lot of guys are using for steel. I think ORD also has a 1 1/2" tube with a 3/8" wall that would be 3/4" ID. You can likely do the same with aluminum if you can get the appropriate stock. Taps are cheap on ebay.