Comstar had a significant presence in several of the Periphery states, where they often recruited. HPG service was available on several major Periphery worlds, not just in the recent House Arano storyline and campaign game setting (where it was on every planet). How much of that remains post-Jihad, I can't say. There are enough independent and "forgotten" worlds that Comstar could easily have a hidden presence, although industrial capacity would be extremely limited due to the lack of many of the facilities and resources necessary to process a wide range of raw materials, and
to produce the countless myriads of smaller components which make up the major systems used in Battlemechs and other high-tech equipment.
I could picture Comstar having a network of jump stops which bypass any inhabited or regularly visited systems, in order to run a clandestine "empire" invisible to those outside the organization. It would still be pretty sparse and weak compared to what they once controlled, and they'd still have to root out any remaining WoB remnants from those systems.