Focus on a niche market first--whichever industries/topics your writers are most comfortable with--and find businesses there.

Research from the Content Marketing Institute shows larger companies (1000+ employees) are more likely to outsource some of their content needs.

Don't forget that although writers are in demand, today's content market is not only verbal; it now has a highly visual emphasis. Look for writers who have experience crafting visual content: video or video scripts/storyboards, infographics, etc. so you have something more to offer clients.

To start finding clients, keep in mind that B2B services are exchanged as part of a relationship, not as a commodity. Most of your clients will come as referrals. Use your current network to get referrals to potential clients. Get to know the people in the niche/s you choose, not just the niche as a whole, and you'll probably notice referrals coming your way through them, if not direct contracts.

Use your website as a referral tool, as well, by building up a body of content and offering a "lead magnet" to grow a subscriber base you can keep updated by showcasing your writers' expertise with articles of interest to them and notifying them of your company's changes and special offers.

If you have any questions about tools and strategies, I'd be happy to talk it through.