ArtPahl - Likely the lack of response is due to the privately made National Ordnance receivers being considered poor quality, dangerous, 1970's - 1980's 'knock-offs' of questionable metallurgy.
There is no historic and little collecting interest in the National Ordnance rifles. The receivers are regarded as 'time-bombs'.
The main value of a National Ordnance rifle lies in stripping it to salvage the stock, barrel, bolt and other original GI parts.