Thanks for the information.
I don't want to give you a false impression Feedori, if the only place to buy these is from player listings I probably wont as player listings tend to be highly overpriced.
I am surprised that you can buy basic versions of all the other upgrades from vendors and find them as drops where these exclusively rely on a crew skill though.
I feel the crit success chance is entirely too random, I'm level 16 on my Guardian SynthW, around 90 crew skill level and in order to get a blue schematic I need to create on average 5-7 greens, in amongst those there tends to be one exceptional, that said with the blues I have ground out a few for the purple schematic (more success prior to the last patch) but some just happen to be a first time exceptional.
Again, with that said I've produced and broken down about 30-40 pairs of one specific green bracer with no schematic to show for it to date.