You would be best off to not use brass fitting and especially not to use compression fittings.
There are reasons compression fittings are not approved for brake hydraulic.

You can buy brake tube by the roll and I have always been able to get the fittings out and reuse most of them.

You can also get pre-flared lengths of tube, many times the store will have one long enough to do the rear, maybe not in the proper metric ends though.

I would not expect you could get a factory prop valve quick, I am not sure of what circumstance you would need one quickly. I am not aware of them springing leaks, the failure mode is to just stay on a low pressure setting and give insufficient amount of braking.

i had one spring a leak on the red truck.found a replacment in a junk yard.