As far as I know, rear, dual side case mounts were never available for our SW's from anybody. There is/was a Honda branded rear right side mount (I have one) but I understand these are hard to get now ... maybe discontinued. Check out Fehling Luggage (Germany) as they still show them on their website.
Personally, I use a GIVI E460 rear top case and the right side rear GIVI mount with one GIVI E21 side hardcase. I also have another GIVI semi-hard case I can swap into either holder but it also is discontinued (it has wheels, an extendable handle and doubles as my airline carry on luggage when needed).
If you're insistent on dual, rear mounts, I'd buy a set off of CraigsList for any MC and take them to a fabricator to have them reworked to fit your SW. I did that with our Burgman 400 for a total budget outlay of less than CAD $100 (about USD$75). But it took me a few months to fins a used set that was affordable enough to make it worth my while.
Good Luck and let us know what you end up doing.