Go to the airfields in person, dressed to impress with a smart CV in your hand, and keep pestering the schools you really want to work for. They will have a vacancy eventually, you need to be familiar to them when they do.
Do you have any friends that are instructors? perhaps you could get a recommendation.
Or, go to the place you did your FI course, asking them for a job or a good letter of recommendation.
How long have you been qualified and how many instructional hours have you flown?