I went on the net to find Tamiya mixing guides!
I bought a bunch of paints and carefullly measured the prescribed colors!
They looked AWFUL!!!! Not even close!
I would suggest getting accurate color swatches of the colors (ask your hobby store or a paint guide for color swatches of RLM colors) and mix your own until you get it right. A lot of their colors are very close to what you need. (IE German Grey is great for interiors and some exterior) remember a coat of future will also darken the colors. (Pay attention to the scale effect to) Always mix a bit ligher.
Good luck
Long live Tamiya acrylics :)