You can still convert your licence at the FAA office but you need prior appointment. Alternatively you can go to Designated examiner and convert your licence. The DE in Kissimmee area charges $40. I don't know the name of DE in ISM but you can get in touch OFT at 1-800-259-2100 and have them arrange it for you. The DE in Winter Haven charges $25. His name is Jon Brown and you call Brown Seaplane base to get in touch with him. Their phone number is +1-863-956-2243.
I hope this helps.