First idea that comes to mind is google handlbar risers. You are sure to get lots of websites. Second is to go to
WWW.roadsidecycles. They have a section with handlebar info. All makes and models. You may find a bar with just the right amount of rise and pullback if needed. Third is to be sure you don't go overboard with dimensions as you might have to get extended cables and front brake line. Just do a comparison of the GZ dimensions and go from there. GZ's all have 7/8 inch diameter bars.
I put "up and back" risers on a Vstrom which made it necessary to re-route the throttle cables just a bit and messing with the brake line for a while.