You don't say where you live so it's hard to make specific recommendations as policy terms can differ from country to country. However, there are lots of reputable companies that write Medical Evacuation Insurance, either as stand alone policies or as part of a broader Travel insurance Policy.

For stand alone policies check out SkyMed, MedJet Assist, MedEvac, Alliianz, TravelMedevac to name a few. You can compare terms, coverage availability, premium costs that are available from almost every underwriter for both stand alone and full coverage policies at www.insuremytrip.com. They even have a Toll Free number you can call to speak with a qualified representative who can answer all your questions and help choose the policy that is best for your particular situation.