Is the sight lost? Is it the kind where the front sight pin just is driven in or the kind where it it has threads and screws in? If the former and it is not lost, it can be just driven back in; if lost, it is easily made. If the sight is lost and it is the screw-in type, you will have to order one. Try www.gunpartscorp.com
. You will also need to buy or make the special wrench.