Where can I find a replacecement mounting bracket for the Hampton bay Versailles 694-573 ceiling fan?

If you are talking about a ceiling box to mount your fan it is not part of the fan kit. Ceiling boxes are stock items at hardware and box stores, your kit attaches to the box. Can you post a picture so I can further talk about this issue?

If you are talking about the ball mount, HD, Lowe's and other stores have some in stock. Go to the fan dept and look at the end cap with blades, hangers etc.