Very, very tough trade to get through Disney, since owners there rarely deposit times into II. Almost the only way to do this would be to advertise on time share boards to try and find an owner there who might be interested in doing a direct private trade. Be advised the going rental rates are very pricey ($2,500-$3,000 a week for a 2BR), so one is looking at using up a lot of points if you could even arrange a trade. The other frequently mentioned Caribbean resort that is just as (or even more) pricey and difficult to get a II trade into is the Westin St. John.
Bottom line: one of the things DVC doesn't tell buyers is that the offical II list includes some relatively impossible-to-get-into properties.
October is low season at Harborside. If you put in a request first with II, you may get it. The thing is that those units generally get deposited all in a block with II, so you have to have your request in before that happens.
You may also want to post a direct exchange on Tug2.net This question comes up fairly often over there. People who own at Harborside are loathe to trade b/c it's hard to get something equivalent. I own at both DVC and Harborside and I have told people over there that IMO, this is an even trade. Good luck!