It might be rebuildable. Look at the area around the piston (inside the spring) if it has the edge of threads showing between the body and that area has a face or indention for a tool, then yes, you can get it rebuilt.
Years that are compatible...85, 86,& 87...and only 750 shocks. 1100 shocks are 1" longer (2.54cm) and are a real bitch to try to have fit, plus they have a heavier weight spring.
Companies that make new replacement shocks are... Fox, WP, Ohlins, and Progressive Suspension. These are available with options like... ride height adjustment, Rebound adj., Damping adj., and an appropriate Spring weight for you and your riding style.
i had the same problem and cant get aftermarket over here in oz...
shock from suzuki was $1200 australian!!!!! so i eventually found a bloke that custom built me one off i think a ZZR1100 for $600.
probably not much help to ya but thought id put my 2 cents in anyway!!