Denova and TFB ops. Otherwise grind dailies and buy them from GTN. If you are filthy rich in real life you could probably buy a few hundred cartel packs instead. If you have left over daily commendations you can buy the droid schematic and put up on gtn for a few 100k credits.
Thing is they're usually getting robbed by the guilds. Imo they should be dropping like commendations - every players gets some.
Best way to get lots of stabs is to buy them. Do not buy anything beyond 150k, though. I got a good deal of 30 stabs for only 3.5 million. Got it today and almost doubled what i spent by now.