The iPhone App Model Colors (available for free in App Store) contains a database of numerous model and hobby paints, including Sovereign ColourCoats. The app has a similar-to function which allows for cross referencing one brand of paint color to others with a variable DeltaCIE or degree of similarity. I ran the ColourCoat paints with a DeltaCIE of 3 (the smaller the number the closer the match, and conversely).
M13 Deck Red:
Lifecolor RAL3009 Oxide Red
Lifecolor RAL8002 Signal Braun, plus few others. A larger DeltaCIE had more hits
M12 Deck Green:
Vallejo Model Air Gunship Green
Floquil CNW Green
AK Interactive (AIR) RLM 82, plus several more
M20 Baltic Gray
AK Interactive (AIR) RAF Dark Camo Gray
Mission Models Medium Gray
Vallejo Model Air Neutral Gray, plus many more.
Interestingly there were no Tamiya hits on any of these colors.
Have you checked with Toms Modelworks in California? They are a seller of Sovereign paints in the States.