Yep, sounds like mixing your own is probably the answer. I can't remember when I last bought a specific WW2 Luftwaffe colour, as I nearly always mix my own according to requirements. This is mainly due to the same reasons as you - the 'real' colours are not available locally, not in enamels anyway, and most mail order houses have a minimum order quantity for paints (in the UK), which you always seem to need 'now', not wait a week for delivery!
Also, by mixing your own colours, you can get the colour/tone/shade to match the particular aircraft being modelled. Too many people get hung up on having the 'exact shade', which is nonsense, as there are too many variables to provide a modelling paint which is exactly right for every aircraft, in every scale, in all weather conditions and ages!