Complete archive of BIOSes for AmberELEC (and UnofficialOS) that match the hashes it is looking for.
At least they matched on my RG351P running AmberELEC version 20230203 Panda Conspiracy at the time of writing/updating this README.
In case there are updates, I'll try and tag it to the same AmberELEC version/date.
Basically, just dump the entire bios content into the bios folder on your SD Card.
The neogeo folder goes into the root of your SD Card.
Open your AmberELEC settings and go to Game Settings -> Missing BIOS Check (it's on the bottom of the menu). It should say "No Missing BIOS Files".