FYI: Temporarily leaving this post on the home page.
The song can also be purchased on itunes now. You have to search for the song using the Korean Title, 없이 못 살아. It will pop up immediately. Its selling for 99cents on the Canadian itunes store (probably the same for other countries). Lets go all out and support.
If you are having challenges with using Melon, you can also try purchasing it on Soribada. The steps are are a lot easier plus everything is in English.
FYI: Requires you to buy a package in order to purchase music on the site. Basic package is $6.99
3. Melon (buying and streaming)
FYI : The process is more complicated if you live outside Korea. Would recommend using the other 2 options.