Well, I don't have any recommendations for you but it sounds like you will make a good tandem team. (I think though that the DisneyWorld Boardwalk Resorts has tandem rentals.)

I don't think it will take you too long to determine if tandeming is foryou. It is important that you like each other, trust each other, and have similar expectations for the tandem experience, i.e. one of you wants to ride 30 mph for 85 miles and the other just wants to toodle along at 8 mph for 10 miles, not a good mix.

Try contacting your local bike clubs, chamber of commerce, local bike shops also, they might know where in your area you could rent. Though not necessarily a vacation spot you may have come convenient resources close by for renting tandems. I've also heard that many local bike shops that carry tandems will let you take a tandem out for an extended test ride. We have bike rentals down by the bike path along the river through the visitors and convention bureau, and they have tandems.

Good luck with this great couple activity.