Last I checked a while back, nobody made one for the GSA1200. I have the same bike. Somebody like "Back Up", or something like that makes one now(Maybe), but pricey around 300$plus. I had one of theirs on my KLT and it was good. I do not ride passengers frequently, but my back seat riders like a sleeping bag bungied back there and it does nicely for a makeshift backrest! Randy:usa
I have a back rest on my top case, dunno if you sprung for the adventure luggage.