Any Orion may have a cloak, it is not Cartel limited. Nor are they limited as to how many you can have in a fleet.
Relevant Rule
(R8.R4) CLOAKING DEVICE REFIT: Many Orion ships (but only a minority) were equipped with cloaking devices to enhance their clandestine operations. The cost BPV and cost of operation are shown on the SSD for each ship.
Romulan police ships do not have a cloak. The only Romulan combat units to lack them.
It has been stated by SVC in various topics (sorry can't point to one off the top of my head) that the various Empires have a handful of cloaking devices used by CIA/GRU/MI6 equivalents, but that they disappear into the background and are not available for (S8.0) (pickup) type games. To date I am unaware of any scenarios that feature such units.