You can get propellant for the airbrush without having to use camping gaz canisters, probably buy them from halfords cheap, they're the type used to power those hand held air horns and such like.
Crimson and cream is one of those liveries which seems to be a pig to get right, as you say bachmann and hornby differ slightly, the worst ones for different colours were probably lima as i have a few of theirs and there are 2 distinctly different shades of red.
I can't honestly think of a colour off the top of my head that might be close to the crimson but i was thinking of one of the older austin rover colours for the cream, montegos and such like ran 2 colours which may be close one was originally classed as white but was a bit creamy and the other was sort of beige/cream. If halfords don't have a good colour then try one of the other car paint types eg carplan or holts. The holts ones had an adjustable spray pattern nozzle too but may be difficult to find. It may be a good idea to try your local independant car parts shop as they tend to keep stock longer than halfords.
Good luck anyway and let us know if you find a good match.