You can find the lab by exploring for it, do some more quests visit some more people maybe you'll come across it.

I guess you mean the military base. It's a location in the world. Harold can hint at where it is, I think, otherwise you might get directed there for another quest, or you could always look for it on your own.

Once you return the chip the overseer tells you to seek out the source of the mutants, you can stumble upon the military base yourself southwest of Vault 13.

Just to clarify, the reason the mutants are gone it's because they all die after you took the chip without making a replacement for the bomb.