try the internet

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You might have to order them above is a link that gives instructions on how far in advance to order and to plant.
Contact some of the wineries for information.
I live in Missouri Wine Country
People here tend to be less competitive and secretive about where to purchase.
………California wine grape nursery………

According to everything I have read thus far about purchasing root stock for growing wine grapes you must belong to a group of wine growers. Otherwise you’ll just have to buy regular grapes to make wine. It’s late in the season but I know Walmart and Home Depot have the root stock.
Good Luck

Trees of Antiquity is a great source for hard to find, heirloom and organic fruits for the garden. I’ve used them several times for ordering apple, peach and blueberry plants. I’m pretty sure thier grape vine selection includes a few wine varieties. They’re mail order, but I think they have several nurseries in California.

check your local stores: Walmart,Lowe’s,meijer, home Depot Kmart have seen them at all of them.

I would Google “grape vines” and see what I got. Probably have to buy from a CA supplier or face import problems.