How would the default skin file be a vector file? There is all fades and practially only bitmap fades which are unlikely to be possible with anything vector. If someone wanted to recreate the skin in vector, that'd be a lot of work, but it wouldn't look that great.
There is no vector skin, and I don't see why you need one? If you want to put the shadings and stuff over your design, you just put the default skin over your design, and set it to "Multiply". That will make it look right.
But there is no need for a vector default skin.