GENERAL: Materials \ Painting

...for metal or wood

Majority of the cockpit in Boeing 737 is painted on iron gray, RAL 7011. You can easily order it somewhere on Internet, however "Colours: Dark Gray Mat" from Castorama is also good. It's cheap and perfectly matches the other elements painted on RAL 7011. I suggest to take a can of 2.5 liter.

...for metal\plexi surface

You may also need spray for painting small plexi elements or metal parts e.g. screws. Leroy Merlin or Castorama offers great choice of RAL 7011 paints.