Hi @spacewindow
This functionality is not part of the ACF plugin. Where is the RoyalSlider data stored? In custom tables in the DB?
You could use a basic select field, but then hook into the load_field filter, run some custom SQL to find your custom choices, and then update the select field with these values.
Tutorial: http://www.advancedcustomfields.com/resources/tutorials/dynamically-populate-a-select-fields-choices/
Thanks
E