I have a similar problem with an iMac running mountain lion. Did you ever solve the issue?
The disc included with the printer would not work to install the software. And even though apple says it has the software when you look up their master list of supported printers, I am getting the error message of "Can't install the software for the Brother DCP-7065DN beacuse it is not currently available from the Software Update server."
The only suggestions I have seen so far are a) to unplug it and try again -which has not worked so far, or b) use a generic printer driver -and according to the directions on this site, my printer does not support a generic printer driver/software.
I tried downloading the software directly from Brother's site, and the install process seemed to work, but I can't figure out where the software was installed, and my computer still tells me it needs to download the software from Apple, and continues to fail when looking for the software.