You gain them from slicing missions. The schematics are really really cheap on the GTN, so don't even bother trying to get them from slicing.
If you have several slicing toons, running the missions (Sliced Tech Parts, crit on Rare Yields returns 2 schematics) is actually quite profitable. Anything other than a Augment 22 schematic will sell for 8-10k on my server. If you want all the schematics for your craft, it does take time. There are 84 Armormech, 105 Armstech and 105 Synthweaving Base (green) schematics, for a total of 294. It took me maybe6-8 weeks to get them all for my crafters. I ran missions until I had about 85% of them, then started buying up any on the GTN for less than 5k. When it got down to my last 10, I even offered up to 100k per schematic on my server's forum, but I got all 10 by running missions in about 1 week. Considering all the "doubles" I got of schematics I already knew, the sale of those more than paid for the number of missions I had to run. In fact, by the time number 294 arrived, all my slicing toons had 7-figure bank accounts.
If you want to see what schematics are available and/or you want to keep track, I have a link to a spreadsheet I used to keep track of my own progress below (GoogleDoc).
(And for the Maker's sake, people, please just vendor your Augment 22 schematics instead of trying to sell them for the default price!)