One of the companies that is on the Stovebolt list of suppliers sells the relay and kick down switch. I think the relay was about $75. I can't remember their name, but they shouldn't be that hard to find.
They appear to be Ford parts but they do the same job.
The last original Delco I saw advertised was in Classic Chevy Int. magazine, I think they wanted $180 for it. As Bill said the headlight relay works fine, the Napa number is AR294.
Fred