A Notary Public is someone with legal authority to witness a signature.
Any notary public may certify your signature.
If you are not able to find a notary public you may contact the US Consulate in your area. They will be able to do this for you.
There is also an online service that will notarize your form and send it directly to us:
https://www.notarycam.com/usabox
and
https://www.safedocs.com/usabox