Czech Models has done the Grumman JRF Goose and Classic Airframes did the J4F Widgeon/Gosling, both in 1/48th scale.
AZ Models is now selling the Widgeon/Gosling kit since Classic Airframes has gone dormant for economic reasons.
There are several float planes in 1/48th scale including the Czech Model Curtiss Seamew, Tamiya Swordfish, Tamiya and Hasegawa both do a Rufe.
Hasegawa recently released the Pete (VERY nice) and Tamiya has released the Seiran and Kyofu, all in 1/48th scale.
Nichimo has done a Jake, though it's rather old and kind of crude (Lone Star Models is about to release an update for the Jake including a whole new fuselage with interior).
Other oldies are the Hawk/Testors Curtiss R3C racer, Ryan ST-M on floats and the Monogram Cessna 180 on floats (it's about 1/40th scale though).
All of the above are injection molded, the Goose, Widgeon and Seamew have resin detail parts.
There have been a couple resin conversion sets to make the Grumman Wildcat on floats (the Wildcatfish).
Other high end resin kits of some of the Schneider Cup racers have been done in the past and are collectors items now.
I know I've forgotten a few others in there too.
Happy Hunting !
