02-26-12: BifwynneHi Bruce,
Where can one source these labels.... Are these re-issues or just old pressings that are still being bought and sold?
Amazon would be a good place to start. As you probably realize, in addition to their own stock a lot of independent sellers sell through their site, offering both out-of-print and currently available recordings.
AcousticSounds.com also offers at least some recordings from a lot of the labels that have been mentioned. Their listings are sortable by genre, label, and format.
Best regards,
-- Al