Some of the various sites I find helpful.

Pontiac 1950's Forum

Pontiac Oakland Club International

1955 1956 1957 Pontiac Safari

California Pontiac Restoration

Pontiac parts from 1926 & up, Specializing in NOS & Reproduction Parts for Vintage, Classic & Antique Pontiacs.

Lincon Batteries

Suppliers of 6v Batteries in the UK

R & R Hotrod Imports

UK Supplier and Importer of Hotrod and Custom, Classic American parts.

Antique Auto Battery

Suppliers of 6v Batteries and Alternators in USA