Sitafloxacin (Japan import) and Moxifloxacin (US import + local generic) are available in large pharmacies like Siam Pharmacy in Bangkok. Minocycline exclusively in hospitals. Pristinamycin in Vietnam is the closest import country; it's currently a blocked export in France. Please don't self medicate and refer to infectious disease doctors if you have mycoplasma genitalium.
Minocycline is not available in any pharmacy in Thailand, you have to visit a hospital and get it prescribed. Pick a hospital, go to its pharmacy and ask for price and availability. If it works for you, book an appointment with the infectious disease doctor and get hope they will prescribe it to you (you'll need to bring test results)