Thinning Railmatch Colours

[McRuss]

Hello,

a friend of mine bought some railmatch enamel colours for me during his holidays in Yorkshire, and brought them to Germany. I wan't to use them with my airbrush. So what thinner I could use best except from the Railmatch ones, e.g. Revell or something else. Because it would be very difficult to get the thinner send to Germany from Britain.
And what ratio should I use to thin it down for the use in my airbrush?

Yours

Markus