If I understand your question correctly, you need to use the APIs to create the list you mention.
In order to get the list of assets you are interested in, you might use the discovery API, in particular I guess geographical search can serve your needs (https://docs.organicity.eu/api/AssetDiscovery.html#operation--assets-geo-search-get
Then, if you don't want to poll the last values of the interesting assets, you can use subscription, based on websockets (https://docs.organicity.eu/tools/websockets/
Adding existing assets to your experiment is not possible, since it somehow goes against the ownership scheme used in Organicity.
Please, let us know if we can help you further.
Luis / Organicity Team