I THINK I KNOW WHERE THIS REPORT COMES FROM

I remember reading a comment post about this years ago and as I recall, the poster even had a map of where the nukes were located.

Threats Claim Nuclear Bombs Hidden All Over U.S.
March 29, 2011 10:04 PM
CHICAGO (CBS 2) – The threats came in the mail and to date, there have been 25 letters that warn of nuclear bombs destroying America.

People who got them called the FBI and CBS 2′s Kristyn Hartman learned, the Bureau’s Chicago office is leading the investigation.

The letter inside said, “The Al-Qaeda organization has planted 160 nuclear bombs throughout the U.S. in schools, stadiums, churches, stores, financial institutions and government buildings.” It also said, “This is a suicide mission for us.”

This myth doesn't seem to have originated with the wingnuts but they have glommed onto it the recent past, as you can see from this 2005 article in World Net Daily.