This topic has been covered here also:
http://www.elantraclub.com/forum/index.php?showtopic=1119
Where can you buy this?
I would first check with your local car part store. If not, it's available online!
Langka.com
Superior Car Care
PremiumAutoCare.com
I would recommend the Langka kit as the instructions are clear and to the point! They give good tips on how to use the product on the Langka website. But what you really need when using these kits is PATIENCE!

Also remember, the kits that are mentioned here are used when touch up is applied. If you have a minor scratch (surface scratch in clearcoat), this can be easily fixed using a coumpoud like Meguiars Scratch-X or Poorboy's SSR's. Better results when applying them with a ROB. (Random Orbital Buffer)
I will keep searching and will add more links to this article.