Here are the locations
Bovver 64 - Once the mission White Lies is completed you will be able to get it. You can also get it in Little Haiti by the Junkyard and in Viceport by a jetty in the middle of the water but it will activate races.
Dinghy - Under the bridge that connects between Little Haiti and Leaf Links Golf Course.
Jetski - On a jetty near another Violator and the Leaf Links Golf Course, one on PIER 1 in Washington Island and behind the InterGlobal Film Studio, Prawn Island.
Jetmax - Docked at the pier at Ocean Beach.
Marquis - Docked at the Marina in Ocean Beach.
Predator - At the Helipad at Hymann Memorial Stadium, Downtown.
Reefer - Docked just in front of a small pier outside the Junkyard in Little Haiti.
Rio - Docked near the VIP terminal at Escobar International Airport. Also south of the Hospital at Ocean Beach and at the pier in the north of Starfish Island.
Speeder - Can only be obtained during the smuggling side missions.
Squalo - Docked at the marina north of Ocean Beach
Tropic - Docked at the Ocean Bay Marina at Ocean Beach
Violator - Near the jetski at Leaf Links
Yola - Outside the Civil Asset Forfeiture Impound where all the boats are locked up.