Some places my snakes have turned up....
In the drawer of my saltwater tank, on top of the movies that are on the bottom of the bookcase - where it's really dark, under my fridge, inside the dishwasher, in between the dishwasher and the counter (I never thought Loki could make it in there, and you can't comprehend how tiny that space is until you see a snake there!).
I've also found Loki basking on a window ledge in bright daylight, and hanging out on my bowflex...at the very top where everyone could see him.

Luckily, I've never had to leave a mouse out, or sprinkle flour, but I've heard that they work very well on the more shy snakes.
Good luck in your search!