In a cobra you could do rare goods trade to earn some credits. For instance this one http://imgur.com/gallery/lkRWdtw. Although I don't know if is still totally accurate.
Waagamici. And other systems around Tamar have sometimes some missions too, worth taking. Assassinations are a good way too. As long as it isn't Killing Grounds ones. I hate those. Edit: I just read it doesn't matter how much reputation and influence you get. Any missions just add a certain percenta...
Fallout 1 and 2 were very good post atomic wars rpgs. Very well written. Even if they seem antiquated now, they were on par with BG2 and Planescape Torment.
Close to Zeta Horlogii there is another system suited for RES farming:
Gende
Around gas planet 1 there are two high res and one low res. The spaceport (15 ships and better high end equipment than zeta) is only over 1 ls away. High Tech.