Due to technical requirements of search engines, it is typically not feasible to release an IP list for crawlers. Crawlers at the scale of modern search engines often span an ever-increasing number of machines that exist in many locations around the world. Because of this, the list of IPs will be very dynamic and as a result would make your firewall rules obsolete in a very sort period.
However, I don't think an IP list should be your primary concern. I assume your security team isn't interested in opening up your firewall to public traffic because these 100 web pages contain sensitive business data. Once you let a crawler access this data it is going to be accessible publically. Site search services typically only allow you to scope results to just a few sites that a user is interested in showing results for.
I believe what might more closely meet your needs is a product like SharePoint. SharePoint will crawl your web pages and allow search all within your intranet.
Eric Carter - SDET - Webmaster Tools Team