If you cannot download via the App Store, you must "sideload" the IPA file.
Sites like iOSNinja , AppDB , or IPA Library often host these files. However, always scan the downloaded file with a virus/malware tool (like VirusTotal) before opening it. These sites are not regulated.
Simply installing the app usually results in a lockout screen. You will likely need to jailbreak your device to apply a "plist" fix:
If your device is jailbroken, install: