There are patch-up automobile paint pens/brush tip at the DIY shops I know. Here at Sengkang, at the basement level their range of colors are extensive. In fact just looking for a red and a black got me so exasperated as each may have around a dozen vatiety of shades just minutely differently from one another.
Try your luck. Best bring your Bromy directly there and compare the bike paint to the patch-up pen color.
I have used these type of paint patch-ups from almost any bike parts conceivable and have been satisfied with their results. Very easy to apply, very quick in drying and very resilient results.