If you used a travel agent, him/her has to submit the form. If you booked via a Carnival PVP, you can get the form from the Carnival website.
To easily check the current prices use this link - CCL Farechecker.
Its easier to use than trying to go through the motions of booking a cruise to find the current fares.
Carnival Cruise Lines:
Fantasy 90, Celebration 95, Victory 05, Conquest 05, Spirit 6/06, Freedom 6/08, Holiday 7/08, Victory 6/09, Valor 9/09, Dream 6/10, Splendor 8/10,Conquest 8/11,Magic 11/11,Triumph 4/12,Spirit 7/12,Freedom 11/12, Triumph 2/13 - The fire cruise
NCL Dream October 2006, RCCL Mariner OTS June 2007