We’ve found a way to connect acquisition metrics, the sources of traffic and Stripe purchase data into a single system.
Try Nerdy Data or BuiltWith.org to find SaaS companies using Stripe
I would either start a Wordpress Stripe plugin, or if you have some cash, buy one of the existing ones. Then you have a customer base, and a relationship with tons of businesses who have already given money once to make Stripe work well with their website.
If you've got the cash for it, Datanyze is great for this type of search. Be warned, they're pretty pricey.