GeoPacks can be downloaded via the Yellowfin Marketplace.
In order to download, you will need a login to the YF website.
We get our polygons from http://www.diva-gis.org. They have administrative areas for every country.
These are available as shape files which is not a format that is natively supported by Yellowfin. In order for use within Yellowfin you will need to convert the shapefiles to WKT which can be done via conversion tools. One tool we recommend is called "ogr2ogr".
More information on GeoPacks can be found on our wiki here: Wiki v7.1 GeoPack Setup...