Some seaplanes

You can install floats under most aviation types. Here is a example of those. Be sure to keep it official. Find out what you can do by yourself and what you need to have done by experts. Official experts. It all depends on the laws of your country.

There are a few seaplanes you can just buy.

I give some more which you can buy from manufacturer or dealer, which are for homebuilt construction or which are in development.