Flat head socket cap screws and machine screws (aka FHSCS) can be purchased locally in stainless steel from any good hardware store or one of the big box joints such as Lowes or Home Depot or Menards.
The hard part is going to find an insert for the drilled out carbon area that used to be threaded. Did it have an aluminum or steel insert that was the actual threaded part or was the carbon threaded, itself?
You could epoxy the hole closed, transfer the location from your cover plate and drill and tap that.
You could also epoxy a small nut to the epoxy, depending on clearance.
Their are clinch nuts and riv-nuts, if you have the room to install them.
There are several other methods that could possibly be applied, but I would have to see the thing in person to know if they would work.