Have you tried different types of litters? Some kitties are very fussy about what they use. We had a male who refused to use anything scented. Some will only use the old non-clumping type. Did anything recently change at your house to make him start this behavior - like a move, new carpet, new baby, new pet, etc??
You might also click on SEARCH at the top right and enter "spraying" - there have been quite a few older threads from people with the same problems and things that have helped. There are also medications to try - some are natural and do not need a prescription (guess i should not call them medications, then!) but also some that the vet can prescribe. Hope you find some answers!!