I have a 2001 nissan pathfinder with roof rails, but no cross bars. Any idea where I can find a set of crossbars to fit the rails?

Try going to www.partconnection.com. You have to pay $10.00 for a year's subscription to their service but you'll be able to search the inventory of all the salvage yards in your area for your specific part. Then you can buy directly from them and save a whole lotta money rather than purchasing a new one from a dealer (this is especially helpful when looking for engine or body parts!)

You can also check the following link:

http://www.courtesyparts.com/secondtier_r50.html

there is a set on sale on ebay right now
http://cgi.ebay.com/ebaymotors/2002-Nissan-Pathfinder-Luggage-Rack-Crossrails_W0QQcmdZViewItemQQcategoryZ33651QQitemZ 8016422910QQrdZ1