Try Dan's Fan City or Amazon for this part. Also might be on e-bay.

It may be your motor run capacitor.It can be found in the top cavity of the fan housing.This component is a small black rectangle block which has 3 or 4 wires attached to it. It can be replaced fairly easily.The approximately cost of this part can be from $5.00 to $12.00.Check on line at Amazon or Dan's Fan City. The component # may be something like CBB61. You will also need to know the size of the capacitor.It is rated in size by what is known as microfarads. The symbol is ufd. Example: CBB61 1.5ufd.-2.5ufd. This component has 3 wires attached to it .A yellow and purple wire on one end,and a single red wire on the opposite end. Good luck I hope this helps.