Ask HN: How can I reach out to marketing agencies in the US?

Hi,

I want to reach out to social media marketing agencies in the US, but not sure where to start apart from searching on Google. I am the founder of Scribblewithai.com. It's a tool that lets user create social media posts using AI. I believe this tool will be really helpful for the agencies as it lets them create content at scale.

How shall I start to reach out to my potential customers? Is there any forum you are aware of that I can post on?