Search for: "Lenovo Windows 7 Professional x64 Recovery ISO" + [Your Model Number]
Unless you want to pay Lenovo for a recovery USB stick (if they still offer it), your best bet is searching the for a verified Lenovo OEM ISO matching your exact model and edition. lenovo windows 7 iso
Here is everything you need to know.
Contrary to popular belief, Lenovo did not delete all their Windows 7 ISOs. They just hid them behind a paywall of sorts. Search for: "Lenovo Windows 7 Professional x64 Recovery