I had a similar problem. I was given a broken Wilton 5x7 bandsaw, it looks just like the HF 4x6 saw, but is larger, takes a slightly longer blade and has coolant and a hydraulic downfeed. It also sells for $900 instead of $150. The gears were missing, but had clearly been destroyed since the gearbox was filled with big chunks of brass. Wilton does not carry replacement parts for this saw. I owned a HF 4x6, so I opened the gearbox and started comparing. They looked the same, but I couldn't be sure because the gears weren't in the wilton. I took a chance and ordered replacement gears and bearings from HF. I think it cost about $20 total. They arrived in 2 weeks and fit perfectly. The saw has been working for me for about 5 years now.
I suspect that if the Wilton 5x7 saw which has several differences from the generic HF 4x6 uses the same gears, then yours probably does too. I'd buy both gears and replace the set, they are dirt-cheap.