Hi @acts238 ,
Here’s a link to a video that shows how to open a Samsung NP 530E5 to replace a faulty DC-In socket.
Hopefully it is good enough to help you to gain access to the CMOS battery.
Once you have it open, find the model number listed on the main battery (unable to see it that well in the video) and search online using the model number to get results for suppliers.
Just a note:
When working inside an open laptop, ensure that you disconnect the main battery as soon as you can, before getting on with any repairs etc, to avoid causing any electrical problems in case you slip when using tools etc. Mechanical damage problems are different ;-). Don’t forget to reconnect it before you close up.
Just because the laptop is turned off doesn’t mean that there isn’t any power still available at various points on the motherboard. The power button is not a power isolating button.