Dell R210 II Firmware Update ISO
Now that the Dell R210 II is unsupported, obtaining firmware is tougher. I was able to generate a bootable ISO using Dell Repository Manager (DRM) which contains the latest firmware updates as of December 2019. I am publishing it here hoping it is useful for somebody.
This worked for my system but your mileage my vary and I am not responsible if it bricks your server.
Dell has a video on YouTube demonstrating how to make and use this ISO:
Dell R210 II Firmware Update ISO Download (December 2019)