Eh I was just giving some help and suggestions, theses links are what we found nowadays.
Since you have dual staged special nuts, make new machined ones if Pioneer does'nt have them anymore
Or if youre lucky find an donnor ??
In 30 years of electronics, i personally never saw in Canada this nut type.
Some of your Pioneer sa506 are on ebay right now, starts at 130$ minus shipping ........ surely you can find a machinist to make a few nuts ?
Good luck.