I have a gs500e that I am going to use for track days.  Where can I find lower handle bars for this bike???  And does anyone know of a good supplier of parts for the GS?

Sherry

Many people find Suburban Machinery's SV650 handlebars to work well for a more agressive riding position.  For more details, and how to install, check Pantablo's page.
http://pantablo500.tripod.com/pablosgs500page/id29.html
Check the rest of his page for some good things you can do with your bike!  

There are other bars out there as well.  Do a search on here to see what other users have chosen for their handlebars.  There will be lots of posts with people who have tweaked their handlebars, but you can sort through them.

If you're going racing why don't you install clip-ons? Early Honda Hurricane (cbr600?) ones fit. FZR600 fit too.  Look for any 37mm fork tube clip-ons.

If you're racing-cliip-ons are the way to go.