Peter T., I still don't see what your problem is. You can start a diatonic major scale on any frequency. It is (as I think you know) the sequence of tones and semitones that makes it a major scale. If you create a scale starting on the second of the major scale, you get a dorian scale. It contains exactly the same notes as the major scale, just in a different order, and the sequence of tones and semitones is exactly the same as in a dorian scale with its tonic on any other note. Hence A-dorian contains A, B, C, D, E, F#, G, exactly the same notes as for G-major. No additonal sharps or flats are needed, but no fewer, either. To build major on G and dorian on A, F# must exist, but no other sharp or flat need exist. Obviously, though, this approach presupposes the prior existence of F-natural; or, put another way, it presupposes some at-least-locally-agreed-upon frequency standard which fixes A, B, C...G in such a way that the creation of an F# is necessary if one is to have a dorian scale with its final (or tonic) was previously designated "A".

T.