So if my broker is based overseas, wouldn't that automatically make the chances of them being regulated by the ISA minimal? Does that limit me to Israeli companies?
Yes, if that broker is offshore it is very unlikely that it is regulated by the ISA. You can open account with an unregulated non-Israeli based company, but your chances of getting any sort of customer protection/compensation in case of some problem would be gone.
You can still, however, open an account with some well-regulated foreign broker. For example, a company based in the United Kingdom - lots of brokers there and their regulation is pretty good.