If you want new axes, I recommend Gransfors Bruks from Sweden. I have their right handed broad axe and I love it. They aren't cheap, but they are lovely tools.

I have bought several axes on ebay, and agree with Shaun that it is a good source. Be prepared to make a handle and it certainly helps to know what size and shape axe you are looking for.

In my opinion, you can use pretty much any felling axe provided it is thick enough right behind the bit to pop the chips off instead of sticking. For scoring, it also helps to have a long handle.