In order to get a sea sparrow in gta vice city you have to collect 90 hidden packages.

There is no cheat for the Sea Sparrow. You only have it once in the game and that is through a mission. All there is is the regualr Sparrow located on the helipad in the airport. you can get a sea sparrow from the lighthouse on ocean beach then get on the sacthez (a moter cross bike) and a mission will come up land, water air race the the last vehicle you get in is the sea sparrow and if you fail the mission you still get to keep it (until you dump it)

Captain Jack Sparrow

Doing the mission land sea and air ace in the lighthouse

sparrow, starling, sea gull, pelican