Disclaimer: I am not a tech, and I don't have a lot of brake experience. However, I have installed my own pads, so that qualifies me as a I-club technical forum expert.
Are you referring to the anti-rattle clip? Located on the bottom side of the pad? In which case there are aftermarket clips, but they come with aftermarket pads (in my case). If you mean that other piece that goes between the piston(s) and the back of the pad, I'd guess the same as T-WRX with the additional idea of heat resistance.