Metal skirting can be found here:
http://www.trekwood.com/parts-search...23+%2F+Keyword
Fender skirting here:
http://www.trekwood.com/parts-search...23+%2F+Keyword
HOWEVER, it would probably be much cheaper and easier to simply go to your dealership (or any Keystone dealership) and discuss your needs with the parts guy.
Most dealers have trailers delivered on a regular basis during the summer season and the factory will put any parts ordered in the next trailer being delivered to that dealer. This will save you the cost of shipping which will usually be more than the cost of the actual parts.