Most Home Depot's carry melamine, but some do not. But understand any that do only carry the cheap melamine foil type. You can usually go to a local cabinet shop and get melamine of much higher quality and sometimes pay the same price -- about $25 to $35 per 4' x 8' sheet.
However, I do encourage you to look at the melamine shelving if they have it. This stuff is usally pretty darn good, much better than what you buy with a full sheet. And in most cases edge tape is already applied and this is done much better than what you can do at home.
For more information on melamine, please see my above reply to your other post.