Mark Baker from AOPA has a BE18 on straight floats. Try giving him a call.

In all seriousness, you'll have a hard time finding 50 hours. These aircraft are not as plentiful as C-152s. Think of the MES aircraft out there: The Grummans, Air Cams, Twin Bees, DHC-6 on Floats and the occasional BE18, PA23 or DC3 on floats. The least expensive one to operate is the Air Cam, but if my memory serves me, they are experimental amateur built which means you can not rent it unless the owner has an LOA from the FAA. Which further reduces the availability of them.

Please report back with what you find, I'm curious to see how you accomplish that.