Help with parts/schematics for Iver Johnson’s Arms .38 SPL

I'm currently trying to help my grandpa fix this Iver Johnson's Arms 5 shot .38 SPL. We can't find hardly any information on this specific model. The only other markings aside from the manufacturer and caliber is a 6-digit code on the other side that's either J16040" or Ji6040". The code is right below the cylinder in the same spot the manufacturer's info is on this side.

We'd really appreciate if someone had a way to get schematics or a website/catalog that sells parts specific to this gun. Also, please lmk if there is a better place to post this. I'll also post on r/handguns.