The American Astronomical Society and NASA have recommended the following companies as sources for ISO-certified solar viewing glasses.
Rainbow Symphony - sells a variety of eclipse viewers including plastic and paper glasses, sunoculars (binoculars with solar filters) and other viewers.
Thousand Oaks Optical - sells solar viewer cards and glasses as well as polyester film. They also sell solar filters for cameras.
TSE 17 - sells eclipse glasses, binoculars and solar film.