Apple's support communities contain extensive threads discussing where to find Lion and how to extract the InstallESD.dmg file. Many users have shared successful methods for re-downloading Lion through the Purchases tab in the App Store. These forums remain active resources for troubleshooting.
If you're interested, I can also show you how to find a similar guide for Mountain Lion or how to set up a virtual machine. Mac OS X Lion Installer - Apple Support mac lion os x 10.7 - installesd.dmg download
Mac Lion OS X 10.7 - InstallESD.dmg Download and Installation Guide If you're interested, I can also show you
Select your USB flash drive from the sidebar and click . Format it as Mac OS Extended (Journaled) with a GUID Partition Map . Select the newly formatted USB partition in the sidebar. Click the Restore button at the top of the window. Select the newly formatted USB partition in the sidebar