I'm traveling from Italy (Ancona) in the middle of October landing in Split early in the morning. We want to go to Korcula the same day (Thursday the 15th) but can't seem to figure out if there is a ferry running daily between Korcula and a few days later to Dubrovnik. Also, what's the best way to make sure we can get tickets . Any advise would be most helpful and apriciated. Thanks!
Check the individual sites for Jadrolinija (http://www.jadrolinija.hr/en/ferry-croatia) and Kapetan Luka (http://www.krilo.hr/en/).
In May, we took the Kapetan Luka catamaran from Dubrovnik to Split (one of the stops on that route is at Korcula). While it's a daily ferry during summer, in October, it changes to Monday/Wednesday/Friday only leaving Split at 7:45AM arriving at Korcula at 10:00AM. The ferry continues on to Dubrovnik and arrives there at 12:00PM. I don't know if Jadrolinija offers any connections to Korcula on Thursdays.
Unless Jadrolinija has something for you, it looks like you'd arrive in Split on the 15th, leave for Korcula the morning of Friday the 16th, spend the weekend there, and then head on to Dubrovnik on Monday the 19th.
In October, you should have no problem getting tickets at the harbor. In May, our ferry was only half full and they were still selling tickets up until the time it departed.
Looks like there is still daily catamaran service from Split to Korcula, leaving Split off season at 16:00 (I took it the opposite way a few years ago, though then another catamaran called the Krilo Jet was running the route).
http://www.korculainfo.com/ferries/catamaran-korcula.htm
If there isn't catamaran or ferry service available on the day you'd like to go on to Dubrovnik, there's always a bus from Korcula that leaves early in the morning - check buscroatia.com for times.