The Canadairs are more than just amphibians - they are all certified by the USDA for water tanking like a land 'plane & have the hose inlets as standard.
The current number of aircraft in the US per Bombardier's website is:
"The size of the Superscooper family in the U.S. consists of six CL-215 currently operating across the United States, particularly in the northern region and in Alaska. Two of them were purchased by the Sate of Minnesota and one, by the State of North Carolina. Aero Flite, a private operator based in Kingman, Arizona, purchased three CL-215 in 2003. On the lease front, there is a long-term agreement between the Los Angeles Fire department and the government of Quebec, Canada for the services of two Bombardier 415."