I definitely recommend trying something like BuiltWith. It's going to cost you a bit of money, but you can get a nice list of domains and then start reaching out to those people: http://trends.builtwith.com/websitelist/WooCommerce

Also consider partnering with other sellers of WooCommerce items. I own a site called https://wpovernight.com/ and our plugins are running on well over 50,000 WooCommerce stores.

Finally, consider releasing a free version of your software as a plugin on WordPress.org. It's a huge (and free) marketing channel. Feel free to schedule a call with me and I can give you a bit more advice about ways you can reach a WooCommerce audience. :)