Always back up your device with iTunes 11.0 before attempting any IPA installation. And remember: every time you install a working iOS 5.1.1 IPA, you fight against planned obsolescence.
Finding a dedicated, modern "blog post" for files on iOS 5.1.1 is rare because the software is now over a decade old. However, there are excellent active communities and resource hubs—like r/LegacyJailbreak and the Internet Archive —that serve the same purpose for vintage Apple enthusiasts. Where to Find IPA Files & Info