These sites all have parts diagrams, some of them more useful than others.
kawasaki.com for part numbers - See OWNER INFO --> Parts Diagrams
Cheap Cycle Parts
Old Bike Barn
New, used, junk, bargains; it's all there on eBay. Make sure you know what you're getting, and pay careful attention to the shipping charges.
Individual stainless steel fasteners. Also, complete stainless kits at their home page.
Pro-Bolt (tasty nuts)
Higher-quality nuts and bolts, aluminium and titanium bolt kits, and colored fasteners.
Fairing bolt kits and other hardware in many colors.
See Replacing body fasteners/bolts
Junkyards, err... Used Parts
Our classifieds There are often several members with bikes they are parting out.
eBay Search ex250, ex 250, and/or Ninja 250.
Cycle Recycling Search Service
Also sell new parts.
Also have a link to Nationwide Parts Dealers.
Also sell new parts; on eBay, too.
dmoz.org Salvage Yard Guide
Bike Bone Yard
Used parts and complete bikes.
A & J Cycle Salvage
Also have new parts and accessories.
Additional used parts: Googling "used motorcycle parts" will turn up lots more choices. It may require some phone time, but if you can't find what you're looking for used for an EX250, you're probably not trying hard enough.
Please check this page.
The Tool Warehouse