Obviously you’ve never lived in Sierra Vista during the rainy season.
South of Tucson or so, it only rains once a year. For about four months straight. It’s awesome. An amphibious anything begins to sound like a solid idea. 
There are a bunch of flying boats in various stages of reconstruction at the Carson City, NV airport. They look like old US Military planes, most likely the Albatross or similar. A few years ago, at the “open house” type event, they had one open and you could get inside it and look around. I’ve heard they are retrofitted for rich Middle-Eastern customers with deluxe interiors and such. I’ve seen one flying over my place once.
I also saw one sitting on the runway, engines removed and tipped back on the tail after a snowstorm weighted the tail down.
The company might be Weaver’s. Look em up. If its not them, they can probably tell you who to contact to get your super-deluxe flying boat.
You can get Grumman Gooses (Geese?) retrofitted with turboprops and modern cockpits and interiors from Antilles Seaplanes today. Are they large enough? There’s a market even today, in the Pacific and Caribbean islands.
If not, if you’re talking Boeing 314 or Short Sunderland size, with a new design, that’s only a matter of having a large enough hangar for construction. There are custom shops who will do any of that if you have the money. There are no 314’s remaining, but there’s a (military) Sunderland at the RAF Museum in Hendon, London, if you get the chance.
The elegant image of the prewar ships (Pan Am, mainly) was for advertising (shocked, aren’t you?). They were as noisy, drafty, and vibration-plagued as contemporary landplanes, except that they subjected the passengers to it for many more hours. Fares had to be expensive to cover their costs, forcing them to cater to the high end market, and thereby forcing the lines to advertise time and convenience as well as provide the kind of personal attention that those passengers expected.
Well, they used to operate out of Rose Bay on Sydney Harbour, which is very close to the city centre. I could see it almost being viable for commuter runs on Australia’s eastern seaboard. Security for a small, slow plane might be a bit easier than for conventional air travel, and there are no long transfers to an airport. Even something like Newcastle - Sydney might be ok for business passengers (there is a seaplane doing similar things out of Rose Bay).
Get a water taxi to meet the plane, and Joe Businessman can be in the business precinct of Sydney ten minutes after landing.
The more I think about this, the more I think it could actually work… now, if only I could win Super Ultra Lotto to get the venture started…