| Not all paint suppliers can do aerosols. I work for the largest paint/bodyshop supplier in the UK and most of our branches don't do aerosols, they just mix the paint in pots.
I'd head down to Halfords and get a couple of cans of plastic primer, some liquid yellow paint (it won't matter if the match is slightly out because the dash doesn't touch the bodywork anywhere so it won't notice) and some clear lacquer. | 
