naw, just get one out of anything, it'll be much harder to find one specifically from a '02 xvan. it'll need to be tuned for the VATS and other stuff anyways, so its no harder to change the OS at the same time.
they came in MANY MANY vehicles from around '99 to '08. mine came from a '02 camaro I believe. you can find them in junkyards, classified ads, eBay, swap meets, anywhere carparts may be found, just look for 12200411