It will be hard, as you have said, to find information on "security infrastructure." The reason being, this comprises many products to include: IDS, firewalls, routers, antivirus, content checking, switches, servers, policy, procedures, disaster recovery, incident response, etc.
Security infrastructure is more like all the systems working together to mitigate risk to malicious activity from both external and internal sources.
Try: www.nsa.com, www.cisco.com, www.issa.org, www.infragard.net, www.searchsecurity.com and any other site that deals with information security. More or less, in the real world information security covers the security infrastructure.Hope that helps.
For more information on this topic, visit these other SearchSecurity.com resources:
Chat Transcript: Internet Security: Securing your company's infrastructure
Best Web Links: Infrastructure and Network Security
Ask the Expert: Placement of security solutions on a network
This was first published in February 2002