It is simply impossible task to achieve for now. You are about to try NetFlix type of blocking. It isn't complete too and NetFlix will fail in this ambition as VPN's main motive is to make sure information available on internet shouldn't be limited to certain location. Why you need those blocking tools for your website?
If you still want to block, you can try this:
First create login for your site. Make sure that only those who login can view information on the site.
Now, the signup shouldn't be open for all. Make sure that it is only based on invitation. If someone like to join, they should be directed to invitation form with email address. So, they can be tracked by the requested IP used to fill the form. After your final decision, you can either accept/deny account creation.
Make a note of it on the login/create account page.
Create login history for tracking location of logged in members. So, you can block those who are login from other areas.
Done.
Even if you try this, your signed up members will be in trouble when they travel as they won't be allowed to login. Please proceed this with caution.
