There was a Beech 18/C45 Expeditor kit released not too long ago Charles - I'll see if I can find it. Not sure about floats, or a kit including floats, but these could probably be carved from balsa. From what I remember of the reviews, the kit is fairly expensive for what's provided.
EDIT: Found it. Mach 2 have a kit - Beech 18/UC45/SNB5, includes decals for US Navy and French Aeronavale, priced at £41.40 at Hannant's (UK).
Probably find one at Squadron or similar US outlet Charles.