Which bracket is broken?
If it's the rear one on the shock bolt, the MR175 unit will work if the small top tab near the shock bolt is bent flat or ground off. It's actually a heavier-duty bracket than the OEM MT250 one. I put one on my friend's MT a few months back, it worked fine.
http://www.ebay.com/itm/HONDA-MR175-MR- ... 5c&vxp=mtrIf it's the center rubber bracket, this place may have something that will work if you can't find the OEM one:
http://www.vibrationmounts.com/Products1.htmSomething similar to the V10Z2M305DM06 may work for you.
Ray