In search of a hat....

A witches hat, that is.

I have been looking all over the internet for either a nice ready-made hat that comes in specific sizes or else a tutorial for making my own. The problem I'm having is that all the hats for sale say "one size fits most" and well....I have a big head! And as far as making my own...I am really more interested in decorating a hat than attempting to make one totally from scratch.

Does anyone have any suggestions? Ideas? Websites or retailers to recommend? I'm running out of time here!