Targeting companies with $1million+ in revenue is not ideal. For a premium content service, you'll probably need to look for companies with at least $4-5 million and a dedicated content marketing manager. Search for content marketing managers in your niche on LinkedIn.

Keep in mind you'll be competing with content factories like Brafton that offer turn-key content production in volume for only a few thousand dollars per month. If you're competing on quality with a high price, you'll need to clearly explain why your service offers better results.

You could try building relations with the big advertising agencies. They have access to huge consumer brands who are all jumping on the content bandwagon. These brands have lots of money to spend.

The agencies can provide a steady pipeline of work. They can help build your portfolio of brands while you're relatively unknown. Once you build a profile, you can start approaching the brands directly.

I would stick to companies with $10m+ in revenue. The cheapest customers are also the most demanding.

Having a good definition of who you serve is the perfect place to start.

Could you define it further..? Do you specialise..?
Really drill down.

How to find those people?
One of the quickest low/no cost ways to find your target audience would be to use LinkedIn.

You have access to a database of C level decision makers & most of the time direct access to them.

Join industry related groups - posting samples of what you do to generate inbound enquiries.
Post calls to action in each example to enquire about your services

Once your a member of relevant groups you can also use the search functions to find those perfect customers and proactively connect with them.

Doing this the right way is a whole course in and of itself. Just know that through linkedIn you can connect and connect any and all of your perfect customers worldwide.

Good luck
Phil

(a) Prepare a list of influencers (online, in your contacts) and pitch them your product seeking directions (not services). Alex shares some really useful posts on how to reach and engage with influencers, at his blog: https://www.groovehq.com/blog
(b) If you have written as guest author at some premium channels, share the URLs in your story. For 'content specific' services, many premium companies are interested to see your voice so far. Most of them are open to good quality guest posts, you can offer to write for them
(c) If influencers are talking about you, and your current online presence starts some engagement, your target audience/people would chase you, rather than you finding them! :)