A couple of places come to mind although neither has exactly what you are looking for. That is no Hobie 16s or 18s.
Calema is in Kelly Park on Merritt Island. They have a Prindle or two for rent (along with just about everything else for the water). The last time I saw the boats they were still in pretty nice shape. Calema is on the Banana River which is pretty wide there and is a nice place to sail. You would not be sailing in the ocean. Tinho Dornellas and his wife Susie run a first class operation and Tinho is a world class windsurfer.
http://calema.com/The other place that comes to mind is Clearwater Community Sailing Center. They have a lot of boats for rent that include Hobie Waves and Getaways. The rotomolded boats seem to be much more common in rental fleets They’re more durable. I know. I own a Wave. The sailing center is located on the north end of Sand Key and faces the Intracoastal which is also fairly wide there.
http://www.clearwatercommunitysailing.org/Unfortunately I have never rented a boat from either of these places since I’ve owned a string of Hobie’s. But, both are highly regarded. I hope this helps some. Good luck and enjoy.