The 'Federal Writer's Project' was a Works Progress Administration affair, and employed a surprisingly large number of noted authors during the Depression.
You'll find the series in any of those Public Libraries designated as a 'Government Repository' - usually located in the larger cities.
Generally - the books can be acquired as 'Inter-Library Loans' - but 'may' be required to be reviewed at your library and not at home, since they're viewed as valuable reference material, and highly pilferable.
Occasionally, extra copies find their way onto the market - but locating them is a matter of luck.
Good Luck!
Vaya,
Scouts Out!