The ICS is a central hub for all nations, try checking here for story leads.
It's possible to trade between pilots, you can exchange goods between your ships, have them arrive at the same point in space and you will have the ability to [exchange] with one another.
Trade ships are unarmed. You can make a quick buck by attacking neutral trade ships and no government will get involved. Now all you need to watch out for is your conscience.
If you can't find what you are looking for, perhaps a Pirate nation planet might have it? Of course, you will need to convince them to let you use their markets.
If you can't find the right story on a planet chances are it was recently conquered by another nation. Try checking planets that used to be under that nation.