It's difficult to give a recommendation without knowing exactly how this BJT is being used, but *most* of the time the specific part isn't too critical.
The package - TO-126 (aka TO-225) - is practically obsolete, but DigiKey, somewhat to my surprise, lists about 40 parts in stock in that package. A few possible substitutes from that list are MJE171G, KSB1151YS, BD440S, BD788G, 2N5195G.