There are two standard matching systems, Pantone an RAL. The latest is being used more by paint and filament as it does not require paying royalties.Therefore, RAL will be easier to find.
Platinum Gray (Apple IIgs, IIc+, Macintosh II, IIvx, Macintosh Color Classic, Classic II, IIci, IIcx, LC)
LVP Powder paint RAL 7044
This is a work in progress.