You have to make them fit, i bent mine and screwed it to the bottom of the tray? you should find them in most bike shops but if not here's a few links

http://cgi.ebay.co.uk/Rrsend-Universal-Number-Plate-Holder_W0QQitemZ8053326954QQcategoryZ9946QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

http://cgi.ebay.co.uk/RRSEND-TAIL-TIDY-BY-MOTRAX-gsxr-cbr-zx6-zx9-r1-r6-rsv_W0QQitemZ8053780514QQcategoryZ9946QQssPageNameZWDVWQQrdZ1QQcmdZViewItem