Is there any M.A.S.H (the series) fans out there that can help me?

No, I don't think they ever played "Paint It Black" on M*A*S*H. The series took place during the Korean War, and The Rolling Stones weren't around then. And I'm not sure of the actual name of the episode you're referring to. But the guy who sang and played guitar in several episodes was named Captain Spalding, and he was played by Loudon Wainwright III. He has albums you can buy, and several are on Amazon. Hope that helped!