Go to the source - i.e. monitor government sites that list new company incorporations and then call the companies with your pitch. In the US that would be the Secretary of State website for each state.

I exclude the geographical condition for the answer. To sell your services to potential customers, you must be clear about who your customers are according to your product, without delving deeper. Is your customer for your product a B2C or B2B customer? Once that is clear, you can determine what your customer is willing to pay by checking the price median for similar products in your target country or area. That gives you the price range. Then, consider why the customer should buy your product specifically. What differentiates your product from other providers, and why is yours better than the others? Write down all these points and put yourself in the customer's perspective to consider whether you would buy this product.

I think it depends on business type. For example SAAS is a type of business that may need SEO but some Startups don't need it at all. You should concentrate on your ICP as a step 0. Having an understanding who is your target audience is the best way to start. As you will have this understanding you'll just have to find communication channels with these companies.
It would be great if you'll have your own website on the first page of Google as you'll be a living example of your SEOs efficiency.