If you can't buy one from the manufacturer of the bush hog, the critical details are the shaft sizes and the shaft length (particularly the length of the vertical shaft that drives the blades), and then bolt pattern on the flange that bolts to the deck of the cutter. Shaft size tells the story of the rating of the gear box. If this is a 6 foot cutter or less, I would imagine that you could find a gear box at Tractor Supply that would run it, just check the shafts and bolt pattern. I bet that there is a factory in China that is turning out 5-6 ft cutter gear boxes that fit 75% of the machines out there. I paid $125.00 for one about 8 years ago from Howse Equipment in Mississippi.