1981 380sl alternator belt tensioner

I’m new to this group as I recently bought a 1981 380sl to fix up. While going to replace the 5 accessory belts I noticed that the bolt used to tension the alternator belt is missing. Maybe it backed out over time and fell out 🤷🏼‍♂️. Does anyone know a part number for that bolt or where I could look to replace it?

Thanks in advance for the help!