Need help identifying & replacing old Cutler Hammer 15 A 3 pole subpanel breaker

One of the breakers in my home subpanel that feeds 1/4 of the house is bad. I've searched high and low for a replacement. The subpanel gets two 110V feeds from the main panel. Each 110V wire attaches to the line side of the CH breaker. There are 3 internal 15 amp breakers that feed 3 circuits in the house. Please see attached photo. Info from the breaker is: Cutler Hammer 3 pole breaker Type MB 15 amp The left one has an "Issue No. M-62" label