OpenRA

Finally found it. C:\Users\[your username]\AppData\Roaming\OpenRA\Content\ra\v2\conquer.mix

Should have known, if you can't find a file, check AppData Roaming...

I've found and opened many of the sprites at OpenRA\mods\ra\bits, but this doesn't seem to be an exhaustive list. I also checked the \mods\c&c\bits dir in case they're recycled from there but nope not there either. Where are the missing sprites?