3.6.0 on pixhack V3x

Good day all

I am having problems with my one pixhack V3x. Its USB port does not seem to activate i.e. I cannot power it via the LED/USB. I want to check that this is not firmware related.
They come out with 3.6.0-rc12. I have loaded 3.6.10 and would like to revert back to 3.6.0-rc12 but could not find it under “http://firmware.ardupilot.org/Copter/”.
Where would I find this ?
Many thanks