There's two markets that can have Cabal submarkets in Corvus Mode Nexerellin/Vanilla. This is hardcoded; the code looks for the specific names of these markets, and puts the submarket in. There used to be three Cabal submarkets, but the 'main' one has been removed. In previous versions, the number of Cabal sub-markets was dependent on how many Tri-Tachyon markets there were; this is no longer the case. There should technically be a third if you have Interstellar Imperium installed, but DR deleted the market.
Cabal fleets however will still spawn from Cabal markets and in hyperspace around Tri-Tachyon markets, so you should still run into them that way.
Hope this clears things up a bit