Thanks to Wangsuda, for being professional as always. Good advice.
You can diversify by working your way up the food chain, from just teaching the present simple and progressive tenses year after year to the same level of illiterates. Try to get a position teaching intermediates, English literature, writing, older classes, maybe into rajabat and university, to English majors. Become certified as a teacher of IELTS, TOEIC, SAT, TOEFL, etc. Become an instructor in a TEFL programme. If you dare to teach private lessons, find a niche like another nationality, international students, math or science, etc.
A potential employer can always find poorly qualified candidates for basic entry level jobs. However, they cannot find people who taught IELTS to Japanese who were math majors.