Mac user here.

Installed one of these in my mac a while back.

How do I check what the latest firmware for my drive is and update it?

Hapy to run a manual firmware update if there is no mac specific software, but where can I even find out what the latest firmware for this drive is or where to download?

Drive and current FW is: SanDisk SDSSDHII480G Firmware: X31200RL

you can see the FW version using system information. In system info choose SATA and then the SSD. The FW version is listed by revision. 

There is no manual FW update. The only way to update the FW is using the SSD dashboard which is only available for windows.