Is there a US National Wine Registry of vineyards, varieties, and vintages? Would I really have to contact every vineyard in America to get this information?
There is no clearinghouse of all wineries in the USA. There are some that attempt to do this like Wine.com but they do not like to share the information unless you pay for it. The TTB (Alcohol and Tobacco and Trade Bureau) has to track every wine bottled because every label has to be approved by them. BUT, there are caveats. You don't need every label approved every year. If your label only changes vintage year every year and everything else is the same, then you don't need a new label. Also, you can get generic style labels approved that just say the appellation and winery name. You can just put "white wine" or "red wine" on the label. Not many people do this anymore. Then there are blends. If you don't see the blend % on the label you might have to dig more since the TTB doesn't track that kind of information.
You might have some luck extracting this information out of individual states, like the Washington Wine Commission's website. But, again nobody has a complete list of all wines, wineries and varietal information.