I see a circlip listed on bike bandit, part # 6 here, (Ships within 1 to 2 business days)
only 2 parts at the bottom show out of stock
http://www.bikebandit.com/oem-parts/1998-yamaha-blaster-200-yfs200k-rear-brake/o/m146132sch102882
copy/paste the link above into your browser address bar, this viglink redirect on here is being gay
btw, no need for '98 specific parts, all 88-02 rear brake calipers are the same