The standard MS21042L-7 (Cad plated) has been replaced by NASM21042 for Nut sizes of to -6
Larger -7 and up are covered under NAS1291-7 (Cad plated).
Available from pretty much any aviation supply house. Aviall, Duncan, etc....
http://www.coastfab.com/uploads/4/1/...291_rev_13.pdf
https://datasheetspdf.com/pdf-down/N...M21042-AIA.pdf
A safe vendor to by from: (safe meaning everything comes with FAA 8130-3 forms for traceability. No chance of getting Chinese counterfeit hardware)
NUT NAS1291-7
Mom and Pop hobby shops like Skygeek are sketchy on stocking levels.