There are as many reasons why we can't make touch-up paint available as there are many colors. One reason is that we try to be environmentally conscious of storing and shipping hazardous materials. We recommend matching your bike's color as closely as possible with model paint from a crafts/hobby shop, hardware or big box store, or automotive paint supplier. Acrylic nail polish from your local drugstore will also work.
Here is a great video on how to fix a paint scratch on a bike: