Security system Replacement camera

I have the WD four camera security system.
I want to replace one or two of the cameras with a 8mm or 12mm camera.
The company informed me that there are other cameras compatible with this system but they did not provide me with any names.
Please let me know if you know of any cameras compatible with the system.

Hi there,

I added the following camera to my WD system: UNV 4MP IP WDR Weatherproof IR Turret Security Camera with Built-In Mic and 2.7~12mm Motorized Zoom Lens (IPC3634ER3-DPZ28)

Got it via eBay, OK price. Working fine when connected directly to the NVR. Would work via a PoE switch, too. I have two other UNV cameras with a 2.8 mm lens connected.

I would think that other models would work, too, but I used UNV because it is the OEM for the WD system.