B7100 HST parts or assembly no longer available

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I recently bought an older Kubota B7100HST-E (2 wheel drive) with the serial number in the older set of numbers. When I put a 40 inch category 1 bush hog on it and started clearing my lot, I hit a stump and sheared the splines from the HST shaft going toward the clutch. On the Kubota parts web site, neither the parts for the HST (66204-36142) nor the whole HST assembly is available for the older model serial numbers. Can it be fixed, and if so what's the cheapest, easiest way to fix it?

Thanks in advance...