I'm not sure if there is a website but you can normally order all these bits through your dealer. other option would be to take one of the screws into a hardware shop and see if they have something that matches.
Goto to the Yamaha parts centre online and find the part number then google it? I've done this a few times and most bolts and fasteners have common part numbers so readily available mainly through eBay. There's a sticky thread on the forum with the link to the online parts catalogue.