The keys come from the groundskeeper. Speak to him in the morning on a weekday to initiate the previous headmaster quest as well as initiating the finding of the keys. If I remember correctly, they keys are found after the groundskeeper takes you to where the previous headmaster had his accident.
Wow, so they are in the latest update. Anytime I go to ask him he just says "Did I.... must have been drunk, will let you know if I remember where they where" something to that effect. I'm maxed out on storyline and he never changes his speech. So I'd just assumed he has no more to say for now.
