The HY200 series are wide spread and very common.
Google on "HY200 3450"
One hit from this site:
http://www.cnczone.com/forums/showthread.php?t=37870
Another one:
http://www.servotrade.it/en/promozio...id_prodotto=62
You should be able to find these quite easily, second hand, Ebay ...
But I doubt that the motor is defective unless it has really overheated or a mechanical problem: bearings.....
I would first check the driver and the power supply.
Regards,
Luc.