Your job just got more expensive. I've had two die in 20 years.
Take the breaker out, and start hitting old hardware stores.
Search google. There should be a label on it.
To take any breaker out of any box, there's a procedure.
At the top where power comes in: There is a main breaker, for the whole box. This is what makes it a 60A box, or 200A box.
TURN OFF THAT BREAKER.
Verify that everything in the house is dead, even the stove. turn off anything you turn on.
Use a meter to verify the breaker you're dinking with is dead, remove the retaining screw, and pull it out.
Now you can clean the label. Start calling the guys in the oldest phonebook you have. Ask everyone who the oldest hw store is.
Worst case, say fukit, call an electrician, and tell him to put in a 200a box.
siemens is what mine are, breakers are on amazon cheap.