As others are saying, there are a number of companies that provide medical insurance for travelers. However, you may be running into limitations of the policies, such as:
It sounds like you are already overseas? If so, I doubt they would issue a policy "mid-trip"
Coverage is usually for a limited time, maybe 40 days per trip and up to so many trips (if a yearly policy) or for a defined period, starting on your departure date.
Coverage is for emergency/urgent illness and accidents, if you are looking for insurance that would cover an elective, non-urgent, or routine procedure, you are probably out of luck.
If you are resident overseas, or on an extended trip (months and months) then you need to look beyond the "travel policies" and more at "ex-pat" medical coverage. Maybe if you share more about your need and situation, someone might have more input.