It would appear that CX tables are not available for Cloud Services users.
From what I could understand they are hosted in prod in the "wikishared" database. This one itself doesn't seem accessible.
Is it possible to add CX tables (or all this base if possible) to the replicas?
I suppose it would involve getting a security review of the schema to determine what fields can be exposed, and the need to figure out if there is space for the data.
Related: table sizes are exposed at T189088#4241980