Judging my the OP's name and the fact that this thread is in the Pokemon section, I'm sure that it is the guy from the 8th Pokemon movie. oo;
As someone who did some cosplay, as well as knowing a few people who cosplay, I find it easier to make your own costume. Just look at a picture of the character and see what materials would be easy to find, make, or buy. While it would be easier to buy your costume from ebay or elsewhere, there is a certain amount of pride that you get with making your own costume. ^^ Besides, then you can be sure that the costume actually fits you.
So those are my suggestions. Just search around. And I do quite believe that there might be a website that focuses on cosplay costumes.