It looks like Boyer Bransden used to make an ignition for your bike but doesn't anymore- they still might be worth contacting for assistance:
http://www.boyerbransden.com/suzuki.html
I have also seen reports of folks using Powerdynamo with good results:
http://powerdynamo.biz/deu/systems/lists/suzuki.php
http://powerdynamo.biz/eng/systems/7201/72017main.htm
A little over $400