I’m not sure if you are looking for the Rota, Stator or Cover. The covers are now very hard to find, they do occasionally come up on Ebay but not very often and they are very expensive. The Rota however is the same part number as the UK model CBX550 31110-MA3-005. Since the CBX550 is not considered very collectable, these parts can be found reasonably priced on Ebay. I believe this also means that the CBX550 stator will work on the 1100R. I’ve taken a look at the CBX550 stator which does not have the big round connector in the main cable like the RC/RD but since the RB doesn’t have that connector it is not necessary. The other difference is the brush assembly; it is fixed in a different position to that on the 11R. However this assembly is only fixed with a simple tie, If you cut the tie you can then move the Brush assembly to the same position as the 11R then fit a new tie to hold the cables in the required position. I would also check the pin out of the 6 way connector as it may be different to the 1100 but that’s simple to check and I would expect it to be the same.
In Europe there is a CBX400 which may have the same generator but we never had the 400 in the UK so I cannot confirm if that is the same.
Please note I cannot guarantee this will fit but I believe it is possible.