How to get iPhone app that's no longer in the store? I once downloaded an app named "aFuel" from the German app store, but I don't have it anymore because over time I removed it from my phone and eventually reinstalled Windows. The app is no longer available (source). 

How can I get this app back? (Or any app for that matter!)

I might have a PC backup that contains the downloaded app, but I don't know what to look for. If you can point me to a likely location on disk then I can look through my backups for any relevant files.
If you were running Windows 7 before the reinstall, look for the following folders:
\username\My Music\iTunes\Mobile Applications
\username\My Music\iTunes\iTunes Music\Mobile Applications
If you were running Windows Vista before the reinstall, you should look for:
\username\Music\iTunes\Mobile Applications
\username\Music\iTunes\iTunes Music\Mobile Applications
If you were running Windows XP before reinstalling, look for:
\Documents and Settings\username\My Documents\My Music\iTunes\Mobile Applications
\Documents and Settings\username\My Documents\My Music\iTunes\iTunes Music\Mobile Applications
These are the default locations for your apps. If you had changed the location of your iTunes folder in your iTunes preferences, you could search your backup copy for a folder called &quot;Mobile Applications&quot; or for the app's name.