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.
The top level augment schematics are cheap yes, but anything below the highest ones can sell for a decent chunk of change. Not saying they will make you rich over night but when rank 22 schematics sell for less than a thousand and anything lower sells for 15k to 30k...that's significant.
That being said, the top level sliced parts needed for the augments are also fairly cheap. So you you do not NEED the slicing crew skill if all you care about is the top end.