Telephone directory help – genealogical query

I wanted to estimate the total number of people with a particular surname within each State or Territory in the U.S and Canada, so I checked out the search functions of a few on-line telephone directories.

For the more populous states, all the directories I tried (sorry – never thought to note them – my bad) had a cut-off of about 250 entries, so all I know is that there are more than 250 people with that surname in that State.

Does anyone know of a directory or other resource which would help me get round this problem?