Where can you buy a rainbow eyeshadow set?

You could probably buy it from any drugstore/shop or counter that sells makeup. You could get a full palette, with all the colours on it. Some of which you can personalise to suit the colours you want - which could be a good idea for 'rainbow eyes', or you might have to get numerous pots with a variety of colours. You could even refer yourself to a makeup professional to ask where they buy their products - bearing in mind this could cost a lot. Hope this helps.