Your medical is still valid, but you need a vaccination supplement. Check the doctors (surgeons) in your area on the official USCIS site.... you may need to call several of them, since lots of them want to talk you into getting a new medical, which you don't need. Just tell them that you need ONLY the vaccination supplement form I-693A.
Do you have the vaccination worksheet from your medical? The DS 3025? It makes it easier sometimes, because then the doctor in the USA has only to transform the information from the DS 3025 to the I-693A.