Make doesn’t have a module for the particular endpoint to list subscribers.
If the external service has a Developer API Reference/Documentation then you should be able to integrate the endpoints in Make using the generic HTTP “Make a request” module.
You can also suggest for it to be made in the Idea exchange. Don’t forget to search for it first, just in case someone already suggested it, so that you don’t end up creating a duplicate.
If you need assistance in setting up the generic HTTP module, please provide additional information about what you have tried with regards to the external service’s Developer API Reference – how you are setting the connection up, a link to the endpoint are you trying to connect to, and what errors you are encountering.