Ruger is not the best about treating southpaws in an equitable fashion. I write and do many things left-handed so I understand your frustration when it comes to finding lefty specific items. Luckily I shoot right-handed. As for the GSR, I would not hold my breath waiting for a lefty model because it probably won't happen. The GSR as a right-handed firearm is still a niche rifle. A lefty GSR would be a very specific rifle & may not ever sell enough to be financially justifiable.
With that said, I never dreamed ruger would produce AR platform rifles, CCW pistols, & hi-cap mags all for public consumption. So who knows....