CVI Takeover / Integration?

Looking to take over a 10-12 NVR HDCVI system. The problem we are running into is the customer wants to add access control for about 100 doors and integrate the system with the access control product. I am having difficulty finding western access control lines that work with Dahua NVR's. Anyone have an idea to integrate these cameras without a wholesale forklift of the cameras? There are roughly 140 of them deployed at the moment.

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