The best way is to go to tech community and offer them to buy from you.

1) Search digital marketing and SEO agencies from Linkedin and google reach out to them , put your financial analytics or revenue of your business in front of them and ask them to buy your SEO company.
Usually , a medium or large size company might be interested

2 Take your proposal in which you should mention the best things about your company, how it will be beneficial for some one who buy it. Trust me, Take written material with you and meet the tech and marketing related companies near you.

3 Email your offer to all the SEO related startups and persons who you know them can help you in this regard.

4 You can also advertise it in newspaper and classified sites which are popular in your location.