If I had the parts in hand, I could have a suitable adapter designed in about 10 minutes, and have a prototype printed within a couple hours. It's not a difficult part to design.
Either go with the aluminum arm, or buy a new servo. Not having any luck finding an 18t servo saver. It won't necessarily kill the servo. I run a lot of high torque servos without servo savers.
Not sure what you are even trying to do? Do you need a new servo saver for it? Are you trying to put a different servo horn on it? No idea how to help you here.