How many nuclear bomb shelters are there in the us?

For all practical purposes there are no nuclear bomb shelters in the US. However there are fallout shelters, thousands of them. But they won't help anyone if a bomb detonates over their city. They will only help those in untouched cities survive a few weeks to months until fallout decays to "safe" levels. However few will know how to find one, most of the signs were removed long ago and many had their food and water removed.