Where can I find the BMR ISO for Networker 7.6.4?
I did come across NetWorker_184.108.40.2061_Windows_BMR_Wizard_x64_WinPE_50.iso but I'm not sure that can be used with Networker Server 7.6.4
The BMR ISO for 7.6.x series would not be available for download openly. The best way to get them is to open a ticket or a live chat with EMC NetWorker support and they should be able to provide you with the package.
You should be able to restore the backup done with older version of NetWorker with the 8.2 ISO also.