You might have imported all starter sites while getting started with the WP Portfolio plugin. In case you deleted some of the previously imported starter sites, you can re-import them with the Sync option.
You can also fetch newly added starter sites with the Sync option.
Find this setting under WP Portfolio > Settings > General > Import Starter Sites > Sync. Also, make sure to choose preferred Page Builder.
Once Sync is completed, you will see previously deleted and newly added portfolios under WP Portfolio > All Portfolio Items in a draft.