I'm an idiot! I thought he was talking about the pin that holds the latch on. But he's actually missing the shaft that the latch goes on. I think he'll need a complete glass frame, as that's either welded or crimped on to the frame.
Here's his pic with the missing shaft highlighted. Maybe someone else (who is smarter than me

) can help him out and send him a replacement passenger side vent glass frame. Nothing available in the aftermarket that I know of.