"...I just need to find some ECC memory..."
Did the 5900x change? Prior to that model at least, AMD's desktop CPU's were compatible but didn't use any ECC features (like plugging a USB 2.0 cable into a 3.0 port... just compatible). You might want to research this as there was reports a few years back that ECC made performance noticeably worse if errors actually occurred (around 10-15% worse) and didn't correct anything.
