This is going to be one long ass suggestion as balancing it out while rewarding as hell to the game will take some other changes.
First off, caps on demand and supply should not exist, perhaps a rate of growth change at certain levels. But ignored ports should continue to accumulate demand until they will pay fantastic prices for anything just actually get some. This would give props to traders who hunt down out of the way ports.
Secondly, race shouldnt matter as far as ports talking to you, just depending on the relations, they will give you really bad deals, and in some cases below a certain amount, rob you(u pay get no goods). You could also have a factor of which ports will deal with anybody and which ports hold to the racial codes.
Now as this will make trading random and thus hunting a small pool of traders nigh impossible, there needs to be adjustments on the other side.
First off, any port you can talk to you should be able to attempt to attach a scout drone too. If you are discovered u will lose relations big time but risk should be fairly low so hunters dont have to spend time raising relations all the time. Scout drones attached to ports dont expire and are only destroyed during a raid or have a chance of being found daily. Second you should be able to bribe ports of your own race into revealing information on traders that visit there, again this could be similar to a scout drone in report style or something you can pick up only at the port. Lots of options and id love input if people would like to help refine the idea.