If you're looking for this because your ZoneDirector finds the AP, but won't downgrade the firmware, then directly installing 9.12 won't work either.
You can install Solo 104 firmware on the R500. This version is Intermediate Signed, so it will install over any other firmware & will allow your ZoneDirector to install its 9.12 firmware.
If you have some other reason for needing this firmware image (but I'm not sure what that would be) then you can SSH to your ZoneDirector and enable anonymous FTP, then use an FTP client (e.g. WinSCP) to download the R500 firmware (which will be at /ap-patch/patch0000/ap-11n-scorpion/9.12.x.x.x.x/rcks_fw.bl7.main):-
ruckus> enable
ruckus# config
You have all rights in this mode.
ruckus(config)# system
ruckus(config-sys)# ftp
The FTP access has been enabled.
ruckus(config-sys)# ftp-anon
The FTP anonymous access has been enabled.
ruckus(config-sys)#
(Don't forget to disable ftp-anon when you're done):-
ruckus(config-sys)# no ftp-anon
The FTP anonymous access has been disabled.
ruckus(config-sys)#
