A JP is not authorised to witness or certify documents which are for use in foreign countries.
A Notary Public has the ability to handle documents for international use.
If your document is for a matter in Australia, for example, a statutory declaration for an Australian VISA application then you should seek the services of a JP.
If your document is for an overseas matter or a foreign embassy then a Notary Public is the applicable person.
For JP services we suggest a google search in your state or area. If you are in NSW there is a link here that provides a register and other information when looking for a JP: