Thanks for the info.
Yes I have tried searching for National, Matsushita, Panasonic, VP-5263A and any sort of combination that I could think of. I did find some references, on some
Dutch, German, Italian and Japanese sites, but no useful detail.
If it was branded differently in the USA due to the National name brand clash, it most likely had a different model number as well, but would have the same physical appearance I think. I have attached a picture for reference.
I did find the scope advertised in an old Italian Electronic periodical of 1974 though.
I did however also find a complete manual for the National VP-5260A which looks very similar but has an extra sweep control switch.
So I am still looking for a 1974 (approximate) National VP-5263A manual and/or schematic unfortunately.
Hopefully someone can shed some light on this!