Currently, the best source for nationwide LiDAR availability from public sources is the United States Interagency Elevation Inventory (USIEI). The USIEI is a collaborative effort of NOAA and the U.S. Geological Survey, with contributions from the Federal Emergency Management Agency, the Natural Resources Conservation Service, the US Army Corps of Engineers, and the National Park Service. The inventory displays high-accuracy topographic and bathymetric data for the US, and it's intended to be a comprehensive, nationwide listing of known high-accuracy topographic data, including lidar. The inventory is updated semi-annually. Note, however, that getting access to the data is often less than straightforward in the current implementation.