Apple now provides the Lion installer for free, primarily for older systems that cannot run modern macOS versions.

If you need an actual ISO file for a virtual machine or a bootable USB for a clean install, you must extract it from the downloaded installer. Apple Support OS X Lion - Technical Specifications - Apple Support

You typically need OS X Snow Leopard 10.6.6 or later already installed to use this specific installer. Creating a Bootable ISO or USB