Exactly what Emily said. I use photobucket for my icons.

As Rainy said, you can just make one using picture editing
programs.

OR

You can always search for one
on google or look through fan images. If you do use one that you did
not make, you cannot take credit for it.

Well, you can start by using some programs like Photo Filtre, Photo
Shop, and things like that. Or you can use a photo editing site like
Lunapic.com.

And after that its really all up to you. You
can draw the avatar or use an image for it.