It might be impossible to collect that Lore if you didn't do it the first time you took the girls through the Canal (and didn't obtain the alternate upgrade path for the rocket launcher, which is a missable event that happens the first time you go through the canal)
The shopkeeper should still be interactible when he shows up near the truck at the end, he's supposed to give you hints about the second upgrade for the Handgun. I'll have to look into this.