Hey there. I know this is a year and a half late, but I figured there's a pretty strong chance your camera has been sitting around taking up space this whole time since there's no practical way to mount it without that cap. I stumbled on this thread because I had the same problem. I created an account on this forum just to share my story in case it helps you or someone else out.
For what it's worth, I'm in the US, so YMMV, but I decided to contact Hikvision at
sales.usa@hikvision.com, explained my concern, told them the model number of my camera, attached a photo of my broken cap and asked if they could sell me a replacement. It was a Saturday that I emailed them.
The following Monday afternoon when I checked my email, I was met with a chain of emails between four different Hikvision employees bouncing my case off of each other, but CCing me the whole time to keep me in the loop. My request landed in the hands of the RMA department, who told me "We have the part." They attached an order form for me to fill out (a Word document, interestingly), told me the part number which is 190302617 (which is information that doesn't seem to exist on the public internet or stamped anywhere on the part), and told me the part is $15.
That night I filled out the form and sent it back in. The following day, they sent me to a secure online payment request page, with a total of $24.38 USD after tax and shipping were added in. So I paid it, received an order confirmation email, and though I never received a shipping confirmation, it just arrived today, six days later. Keep in mind they did NOT include the three screws, so if you need those as well you may have to explicitly request them. I didn't need them because I was able to take them off my old cap. The set screw IS included, however.
It was a surprisingly pleasant customer service interaction from a company which I know has a bit of a black cloud over them, especially lately, and with an end result I did NOT expect. I didn't expect them to sell me the part on its own nor did I expect it to be so cheap. It was even packaged very securely. It almost makes me feel bad for switching to Unifi Protect. Almost.
I hope this information is still relevant to you. Good luck.
