Here is the link to the Wikipedia page that I found the reference to that event on (no citation, it could just be wrong for all I know). I'm interested to know who the key players were in the run-up to the ban, and how controversial it was in the political context of the Italian peninsula. I've done a little reading about, but I am having difficulty getting any specifics.
(On a side note, I'm running an RPG with some friends set in early 15th century Europe, starting in 1415, if anyone knows of any interesting events that were happening at the time, I'd appreciate it if you let me know about it!)
Depending how much time you have, I would suggest the (absolutely magnificent) "Mediterranean and the Mediterranean World in the Age of Philip II," by Ferdinand Braudel. My edition is something like 1300 pages, and it will clear up pretty much all your questions about anything ever, especially 15th-16th c. Mediterranean politics. There is a lot on the slave trade, which I don't remember off the top of my head and don't want to misquote, but I am fairly certain that it continued (even in Ragusa) during the 16th century.
But seriously I am not an expert on this topic (I do Rome) but the book is absolutely phenomenal and if you like history and that period (and literally can't get enough of it) you should read it.