njee,
I think you can tell a difference between a high end trek alu frame and a klein alu frame, the klein being a little stiffer feeling in the rear end and the welding/brazing whatever is better than treks.
I had an ’02 attitude frame for a while and now have a trek 8500 frame , both the same size … you can see a lot of elements that were in the klein frame followed through into the trek frame.
to the op, there are a few select places where you might be able to get some original stock … but at best it’ll be a few years old and most likely involve importing. I did that for my klein road frame a couple of years ago.
I think as time goes on, the USP of a Klein will be its rarity more than ride features.