Carlos, I did the same thing last year and just finished replacing my mount bracket @ a month ago. I have a 2001 Nitro with a Motor Guide tm. The problem is with the mounting plate the bracket goes on. My plate (mounted to the boat), that the tm bracket goes on is not like the current one they use. Most, if not all today are for the 'quick release' mounting bracket. Which my 2001 tm does not have.
I found a bracket (new) like the one I broke, at a small shop s/w close to home. I took the old one in and made sure it was what I needed. They come in at least two different lengths. Here's the name and number of the shop: Rod's Trolling Motors, Batavia, Ohio. (513) 724-3126
Getting the bracket mounted to the plate on the boat was, to say the least, a real dog fight. The bolts that hold the bracket come up from the bottom of the plate. The plate appears to be permanently mounted to the boat with metal pins. Making tightening the bracket down very tough to do , as the bolts keep turning as you attempt to put the nuts on them. I solved my problem of this by using an epoxy to keep the bolts from turning as I screwed the nuts down.
I hope this in some way helps you? My only other option before I figured it out was to get a new trolling motor and have it mounted by the boat riggers. Didn't want to buy a new tm when only the bracket was broken.