Hi Peter
In my experience it’s not unusual for these indicator brackets to break as you describe. You are correct that the 1982-1984 CB900/750 use the same part, so they do come up on Ebay from time to time. However it is also worth noting that 1980-1981 CB900/750 and 1100RB’s used a similar bracket which is smaller round, the indicators stems were also smaller and of course shorter screws. Look at the link below where I have posted pictures of the indicators from an RB and RC/RD as a comparison.