As much as it sucks, Facebook and Nextdoor are your best options. I hate using both of them, but we get a lot of traffic from both when we have our plant sales.

Also, start a mailing list (Mailchimp isn't great, but it's free for basic, small-scale stuff) and ask people who buy from you if they want to be on it. Plant people are often repeat customers, especially when you add new varieties to your catalog. As long as you limit yourself to only sending out announcements occasionally and not annoying people, that's a good way to build up a customer base.