Where can Ii get a sissy bar?

Hi, I have a 1980 KZ 750 LTD. I have purchased two sissy bars/ luggage racks on eBay and sent them back loosing money each time. I can't seem to get a sissy bar that fits my bike. Does anyone know if Honda CB's are the same size? Should I search for backrests in their models or Suzuki GS's? Any tips? I really want one and their aren't any for sale in the exact year and model of my KZ

I kinda wonder if the rear seat is bigger than stock. ??? maybe not, just wondering if that could be a fitment issue.

I'm not sure if these two items fit each other, but here's a sissy bar & an oem side plate set. I can't tell if the sissy bar bolt holes have the same eye-to-eye distance as the plates. I would ask the seller about the sissy bar to verify the model fitment.

NOS Kawasaki Sissy Bar Plates KZ750 H 1980-1983 K53033-021

80 KAWASAKI KZ750 H LTD OEM BACKREST SEAT