Yeah the prosperity thing put almost as much of a damper on independent trading as the fief efficiency did last round. There's still a couple fiefs on the NA side open to free trade though. The sell locations are circled green and the buying locations red:
The FCC fiefs (yellow) probably have about 25% tax each, the FPF fiefs (bright pink) have 10% taxes and the red DL castle in the south has a 10% tax too. If you're an independent trader, it's probably a good idea to contact clans who's fiefs you're passing by on the way to these locations, so they know you're not going to try and use their S&D.