I suggest direct from TRP if you haven't tried that option.
There are better rotors available than those from TRP, and better PM/IS adaptors also (at least adaptors that will accommodate a wider range of frame/hub tolerances). If the riding environment is all flatland it's not such a big deal, most brands of rotor will work. For steep descents with frequent or continuous braking, larger, thicker rotors offer advantages.
I recommend SwissStop green pads over stock pads supplied with the Spyre caliper.