www.pocketpctechs.com is a good place to start or
www.pdaparts.com.
However as you mention an x3, this is now quite old and to be honest it is questionable if the cost of repair is good value when you consider the cost of buying a second hand unit from ebay or similar.
The lowest cost solution may be to look for someone selling an x3 because they have a broken screen and changing the motherboards thus solving your problem