I had that happen with a whole ring of keys - house, car, office. I had to have copies made after I searched everywhere without any luck.

I found them several months later in a dresser drawer - not my dresser - the one that had been my ex's. I never used this one for any reason, and the only reason I found them, is that I decided to clean out old some old stuff that he left behind.

This wasn't to awfully surprising to me to find the keys in there, since we have an "entity" that visits here and takes delight in making things disappear. But that's another story...........