I normally get paint from a place in Bedford, called "Nu agane". they mix up any paint based on manufacturer, year and color code. I've had very good results- the color match is very very good.
He can't mix a touch up paint but you generally will get better results from an aerosol. Spray some of it into the cap and use a brush to fill in the chips. This way, the paint is much thinner and you'll get better results.
Jon