Columi and Rakata schematics will drop from eternity vault and karaggas palace operations.
Black hole / campaign (26) mods and enhancements can be RE for a chance to learn the schematic, you need to pull them out of black hole pieces that you can purchase on the fleet or campaign pieces that drop from explosive conflict hard mode . You cannot RE the armorings from those pieces since they are slot specific, but you can RE the generic armoring that drops from kephess in explosive conflict.
Dread guard (27) works similarly except the gear piece will drop from terror from beyond operation, then you can pull the mods out of that and RE for a chance to learn the schematic.
Thanks for the reply! Looks like we will have lots of high end PvE in our future !