Hello! Where can I find older RouterBoot (BootLoader) versions? I’m having problems on some rb-s with 3.10 firmware.
What are those problems? We could fix them.
I explained my situation here. The problem was probably in the 3.10 firmware. After many attempts, I was able to do a bios reset, load the backup bootloader, then Netinstall with ROS 5.26(3.07 firmware). The rb works now, and I’m testing it. On some rb-s my collegues already have installed ROS 6.5, but the firmware was not upgraded for a long time(2.x firmware). I would like to upgrade it to 3.10, however, now I’m not sure if it is a good idea. 
I had no problems with 3.07.
A database (archive) of older firmware versions would be a great thing for such situations.
RouterOS has a firmware file inside it, so, you can load backup bios (as you did) install version that this router supports and then “upgrade” bios to version that is supplied with RouterOS you just installed.