Try Hemmings Motor News, a monthly publication found at many newsstands. It has almost any part you could ever need. They have private party classified ads as well as ads from resto companies and salvage yards from around the country.
Also search out any clubs that specialize in El Caminos. Maybe a local club devoted to Chevys. There might be members of these clubs that may have sources or know where to get the parts you need.
Keep an eye on eBay as you never know when another set of doors may pop up. ( Good things come to those that are patient
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