The formula you are looking for is get_field("your_key", "widget_$widget_id" ); where $widget_id is the unique instance of the widget. This can be difficult to grab dynamically though.
I would look into the global $wp_registered_sidebars to see if that contains instances of the widget that you are looking for. I do know for a fact that sidebar data is stored in the wp_options table so you may be able to query that directly to get the unique instantiated widget ID as well.
will get you an associative array for each sidebar and the widgets that have been added to that sidebar. The unique id you are looking for will look something like `my_widget_name-43′ most likely. 43 being representative of the 43rd instance of that widget over your site’s life.