All trigger guards are not absolutely identical. Even an original replacement may fit poorly in another original stock which has previously been inletted for another guard. You may of course get lucky but you may not. That would be one argument for making your own.
If you have the guard which is original to the gun you can cut it between the screw holes so as to preserve the serial number. Having one for a pattern would be very helpful.
I do have a couple extras laying around but hadn't realy thought of selling them.