Using webservice to popolute/search Address Field fields
More than likely, the best approach you can take here would be to add the AddressField reference to wherever it needs to be, and then add in logic to poll and collect address data inside a form validation call inside a module, using a hook_form_FORM_ID_alter() 1 call, when new Entity is created or edited.

This guide provides additional information on using validation calls in Forms: https://api.drupal.org/api/examples/form_example!form_example_tutorial.inc/7