do you mean the part of the barrel arbor that the key fits on to to wind it? If this is the case you would do well to make sure they have not done further damage to the mechanism by using such force? If you know someone who owns a lthe it is not too difficult to make a new arbor.
If you mean the tang that is used to hold on the mainspring, that can be replaced.
Let us know which it is and we can then help further