To answer your specific question, I don't know.
That said, if you want easy access to the highest end ships you'll have to take a commission with someone to open up their military market. Even a relatively low stability market that you have full military access to will offer high end ships for sale, including capitals. Otherwise, it's all just down to luck (sometimes black markets have certain caps for sale, but not at the frequency of military markets) and some ships are easier to salvage than to buy.
Fair nuff. I'm at cooperative with Diable Avionics, I just need to keep rolling the dice to get that Dreadnought. I saw it in the market much earlier in my campaign, will just keep checking.