I'd check Lowes or HD for ceiling fan parts.
Trekwood may have them for 3 times the $$ & their shipping rates are sky high, you probably replace the entire fan cheaper.
I would buy a new fan. We replaced ours and it made a big difference in the amount of air it moved, especially when the air conditioner is running. The fan that was in ours was cheap and you could'nt feel hardly any air movement. If you do replace it make sure you check the CFM rating on the new one which tells you how much air it is supposed to move. The higher number the better.