I seem to have the same scenario going on in the machine shop. Opened a tool box they other day to find a mouse house in the drawer that I removed with the shop vac but, seems like there are a ton of them, and I'm going through Victor snap traps like water with a little peanut butter on the trap pedal. All pretty plump as well but there is really nothing to eat inside the shop so I don't know what they are eating.
I just order a full case of Victor snap traps from Amazon, should be here tomorrow I too tried the mouse killer blocks and like you, they consumed them, pooped everywhere and kept right on trucking. Things are useless and expensive. Maybe I should put out a couple saucers of glycol antifreeze? No pets in the shop to get into it. Might work, maybe... I can shoot woodchucks and possums and racoons but mice are way too small to shoot...lol
Problem with using Glycol to kill them is, they die and then stink whereas the snap traps kill them and I toss trap and them in the refuse can and they are destructive. They like to chew on wiring insulation. Especially the new vegetable based stuff.