We're having a similar issue. There seems to be no host or cluster filter available on either datastore or network.
We circumvented this issue by having someone go through and organize these resources into folders that match the cluster name they're assigned to, which at least allows us to query the way we need to (keeping in mind that you have to query to get the folder ID, and then pass that into the folder filter for datastore/network call). But it would be nice to eliminate that bit of manual work in keeping things up to date, and have the ability to do this query directly in the REST API.