The following sites carry this information. You can order from them too.
http://www.bikebandit.com/PartsBandit/
http://www.ronayers.com/main.cfm
According to GsJack:
QuoteBoth have parts fisches(sp?) to locate part numbers. Bikebandit uses their own part numbers, gives about a 5% discount, and has fastest delivery. RonAyers uses Suzuki part numbers, gives about 25% discount, but takes longer to deliver. I've used both and got good service. BikeBandit when I want a small thing in a hurry and I used RonAyers for the bigger order of parts to fix my wrecked bike last year.
THIS PAGE (http://www.bbburma.net/Documents/GS500_Parts_Fiche_1.html) has direct links for 4 different vendors.