From the picture it is hard to see, i do not think you will find another one easily. if the teeth are very blunt then that is most likely the problem, you could try to file them a little and see if you can get a little more point to them but it could be hardened steel. A good small triangular file might get them a little sharper again to try and see if that is the problem. I am not familiar with the 18-3 feed dog setup, just the 18-2 but that is adjustable and like the normal feed dogs so it could be something else that is worn on your machine??