I've had the same problem. I know the original dealerships on two of my cars. Gustatson Chevrolet, 7th and D streets, Eureka Ca (No longer in business) and Wilkins Chevrolet, 6970 N Military Hwy, Norfolk Va. (same family owned but now Bay Chevrolet)
I have googled and searched and found very little. A few old newspaper ads and a story about one of the owners that was a former race car driver but other than that no luck. Was hoping to find some old dealer pictures like Chick has but so far nothing. Also continuing to look for memorabilia.