@John Martelotti48 Some are importing (with subscribers permission) their list in convertkit but, if you are a startup what I can suggest is to create a landing page and share it to your social media account to gather info for potential subscribers. You can also embed it on your website if you have one so that they can sign up there. Here's a link on how to create a landing page in Convertkit.
https://help.convertkit.com/en/articles/2729499-how-to-create-a-landing-page51