Measure your mount brackets. Go to a dealer and measure a set on a Streetglide or Sportsglide etc.
You in Tassie mate? Reason I ask is I seen a bookface post from a chap in the same predicament, hope you find a cheap solution.
That sucks mate, lost an found sites for the area maybe? Long shot, rough idea where they came off?
Yes, I know where they came off because people had reported that they had been picked up and placed next to driveways along the highway, but by the time I got there someone else had already picked them up.