Not trying to be over simplistic but did you try your local hardware store? If I'm understanding right you've lost a bolt to a nut and bolt combination. Take what you do have and go to the hardware store to replace. Might be a bit shiny but it can get you functionality.
FYI, this isn't a "I told you so" but is meant as help. Consider getting an old dozen egg crate or pie tin to work out of. A clean shop rag underneath keeps things from slipping. Separate parts from tools when working a bench.
Last, agreed with Nhan Le, excellent idea going to the web. Can't directly mention source respecting board rules but just like vintage car parts there are retrofit vintage bike parts available from the bulk bike part distributors. I was surprised what I found for a Strumy Archer 3 speed shifter assembly I worked on last season. Whole assembly, shifter, housing, cable, linkage. Old can be cool but it can get rusty too, which inhibits functionality.