Mary Anne:
Check with your medical insurance provider. As part of their wellness program, or disease management program, or general service, they may have a connection to medical translation services. This is also common in larger hospitals, but they may not have all of the languages you need. Your health care provider or doctor may also have a connection to one.
While your request may not be one that requires a medical translation, if your son's allergy is severe enough to warrant the note, then you should have a note from the doctor explaining the diagnosis, symptoms, and treatment, so that in the event of an emergency you could give the note to the local doctor and not have to worry about making yourself understood or waiting for a translation.