iMac G3 333 Hard Drive Swap

[112345]

I recently picked up an iMac G3 333 and ever since when I’ve plugged it in I’ve gotten the “Sorry, a system error occurred”, which restarting did not solve. There was some talk of the hard drive being faulty when I picked it up, so I’m leaning towards getting a new one as a solution. What would be the best way of obtaining a new working one that would solve this? Optical Disk Drive is also missing, but assuming that is not the issue.