I’ve started to gather together some free Seaplane Base Addons. Also useful for my Goose.
Gives us some options, but of course will take some time to get world coverage!
Here they are (but they’re easy to find, so may not be that helpful hehe):
TFFJ - St Barthelemy/ Gustaf III Airport - Upgrade » Microsoft Flight Simulator (look for the extra separate download on the popup)
There’s a bunch more in USA & Canada but I have not downloaded them yet. Here is the search page: Discover Microsoft Flight Simulator Add-Ons » Flightsim.to