I would recommend a new stem maybe? Finding two face plates is going to be difficult without buying a NOS stem and if it is failing, what is the condition of the rest of the stem? The new Ritchey stems are quite nice they wrap the bar more and look quite spiffy. Most shops aren't going to carry parts like that unless there was a recall and those were replacements for customers but in that case, Ritchey likely would have let you know it has been recalled and would do something for you generally.