Possible solutions;
1. Proxy TCP tunnel as a standalone Windows application that will sit between the INTERNET & IIS and will block IP/IP Range as configured;
OR,
2. If sites are PHP specific, I can get you a single PHP script that will use a MySQL database (or may be an XML) for configuration and block/redirect HTTP requests from IP/IP Range. You just need to REQUIRE/INCLUDE_ONCE the script for all your PHP application (there is a way in PHP INI file to auto include it);
I prefer the second option, because a TCP tunnel may cause trouble in detecting the request originator IP for your applications hosted with IIS. On the other hand, a PHP filter script has the advantage of optionally being used in specific applications and more flexible to configure with. Most of all, a PHP script is open source and you will know what it does.
Regards,
Joy