Re: What was illegal to trade in the early 1500s?
My recollection is that it wasn't illegal to trade items so much as it was illegal to trade in certain places. Spain -- the Microsoft of the 16th-17th Centuries -- made a particular effort to keep what they regarded as English 'interlopers' from trading with their colonies so that their own merchants could maintain what we today would regard as 'market share'.
This eventually backfired when they jumped all over Sir John John Hawkins' fleet of merchant ships at San Juan de Ulua in Mexico in 1569. The survivors were rather ticked off, and swore revenge. Since one of those survivors happened to be Francis Drake -- the kind of fellow you most definately did not want to swear revenge against you -- this ended up working out rather badly for His Most Holy Catholic Monarch, Philip II of Spain.
So the real coup, arialbunrz, would be if you could work with your story so that it was trade in some region where Spain or Portugal maintained an embargo -- rather than trade in some illegal product -- that caused I've found that introducing a concept that was widespread at the time, but could seem weird to modern sensibilities, can go a long way towards establishing authenticity and making the readers feel they've entered the time period in question.