For new ones, you can contact the moderator of this site, www.yamahagenuineparts.com , which is in Canada, or there's
http://www.babbittsonline.com/yamaha-motorcycle-parts, or
http://www.powersportspro.com/pages/OemParts?aribrand=YAM Always good to get a couple of quotes on new ones, as they are spendy parts.
For used ones, I belive there are a couple people selling parts on the forum, you'd have to look through some of the posts...
Rattosh51
YT6800