Interested in buying or swapping for ONE National HRO-50 control knob
and metal skirt, can be any of it's 6 control knobs. I dont' mind if
it's dirty
Let me know what you want and/or need.

Have you tried Mike Tannenbaum from PA?
He sell manuals & Sams but was big into National parts.
http://www.agtannenbaum.com/
GL........
Rich