My 'ex' lives outside of Israel with the children. I have remained in Israel. She refuses to bring them to Israel for visitation, according to our divorce agreement. What can I do?

The best option for you is to file for the enforcement of visitation rights under the divorce agreement in the country where the children live. Even if the other country is bound by the Hague Convention like Israel, this Convention is of very limited use in enforcing visitation rights where there is no abduction involved.