Tip: Have you tried creating Facebook ads with "WooCommerce" (and variants) as Interests?
Campaigns with specific interests and a few demographic filters are quite effective. Especially now that Facebook aggregates data from other online and offline sources.
Good luck! Let me know if you have any more questions!
I explain how to do it here http://linkedexpertsalliance.com/topic/how-to-find-fresh-new-clients-on-linkedin/
If you want to code it yourself, find a big list of domain names. Create a script (I use PHP-CLI) to download the homepage of all of them and look for some kind of meta tag that only WooCommerce has. Load that script on a Linode with tmux and let that run for a few hours in the background. Now you have a nice list of domain names with WooCommerce. If you want to save time, let me do it for you. If I like your service, maybe I'll sell it for you for a commission.
To help in cold-calling, you may want to use a service like www.builtwith.com or www.perfectleads.com. You may also want to go the path of Google Ads. It's been highly effective for many business owners.
Additionally, if you build a free plugin that ties into woocommerce, you can get a number of your target audience to download the free plugin (as long as it's useful, and hopefully pre-sells your woocommerce product/service).
Hope this helps.
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. :)