Now lets get real for a moment, hundreds of RPT flights operate in class G daily. Most airprox events occur in controlled airspace or close to a CTAF. RPT with TCAS must report RAs so there would be a good database of conflicts OCTA as well.
You're just not getting it. Transponders aren't required to be fitted to VFR aircraft operating in G.
A while ago there was a near-collision involving an RPT jet at Mildura, all duly reported and investigated by ATSB, on the basis of data produced by the aircraft involved. The laughable irony is that the aircraft that actually came closest to the RPT jet that day was never seen or heard by the jet and the event was never the subject of an investigation, because that other aircraft didn't have a transponder so didn't produce an RA or TA or whatever A in the jet's cockpit.