Practicing medicine overseas is one of many choices of jobs for retired physicians who are seeking some adventure as well as career satisfaction. There are many organizations that provide medical care around the world, and they can always use experienced physicians. You don't need to make a long-term commitment to living and working overseas—many organizations arrange for physician part-time jobs that last for periods of weeks or months.
Think about areas of the world that appeal to you, and how your skills could be useful in helping medically underserved people in those areas.
In addition to creative Googling, some leads for overseas medical work include: