If you can't find the right key stock, I think you can, the next step is JB Weld. I had the splines wear almost completely off a treadmill drive shaft where the belt from the motor connected, lots of slipping. The splines in the metal pulley were OK so I coated the worn shaft with lots of JB weld and slid the pulley back into place on the shaft. The JB stuck to the shaft, the pulley formed new splines on the shaft and a couple of blobs of JB on the outside edge of the pulley kept it in place. No slippage and no problems with drive shaft of the treadmill since.