Hi Lunar,
Tarozzi rearsets are a good option if you can fabricate your own mounts.
(http://www.fastfromthepast.com/servlet/the-Rearsets-cln-Universal/Categories).
A member from the SR500 forum (http://www.sr500forum.com/forum/index.php) sells a pair of bolt-on rearsets for $325.
(http://www.n-rperformance.com/rearsets.html)
But if you feel like spending some serious coin there are a ton of companies in Japan (i.e. Bore Ace, Peyton Place, WM to name a few) that sell works of art. Japan Webike has a small selection of them.
(http://japan.webike.net/categories/100000_120000_125000_125010_1050125010.html)
Hope this helps.
Kelvin