We're a graphics design company that target WooCommerce, BigCommerce and Volusion users.
If I were you I try the following (assuming you know which stores you want):
1. Play dumb and call their support number and when they answer tell them that you dont know why you were routed there when you wanted to talk to the marketing department.
2. Create an email blast to either firstname.lastname@example.org or email@example.com chances are if it is a small operation the email will be seen by one of the founders/owners and they might take a peek at your offer.
3. Spend a few bucks and buy InMail contacts with Linkedin so you may reach the right person of the company you are targeting.
Or you could spend some big bucks on a tech blog site like techcrunch or get a blogger from a portal like http://www.ppchero.com/ to write a post on your offering