There are products that provide lists of valid addresses in various ways.  Whatever source you choose to pursue you'll need to consider how your users will interact with it and how you will integrate it with Forms.

You can pass the address from forms to workflow to validate the address

You can do lookups on the address fields as the user types, but it won't autofill until you have an exact match.

You can use a third party product with no integration at all, the user receives a verified address and pastes the result into the form.