Not that I am aware of, but you'll probably have better results searching Joomla.org extension directory. Easiest approach is to enable admin approval so you or another admin has to approve the users registration.

Just wondering if there is another way thru CB to restrict geographic user registrations.

No, not without developing a plugin to do this. Besides if you're basing this check off a field a user fills out in registration it's easy to fake.

If basing it off user agent, IP, etc.. that's extremely easy to spoof and actually most browsers come with the ability to block websites from obtaining that data so you'd likely prevent numerous legitimate registrations from passing.

Again, best approach is to enable moderation approval of registrations and manually approve each registration. This times you the ability to review a users information.