Firstly, I see you are from thailand. You could start there. There are 2 there. And secondly, you need to be a float plane pilot to fly one. I am presuming that you are one and that you have flown thousands of hours in open water, reefs, and the like before. If not you are wasting your time. Having said that, try the Seaplane Association of Australia. There is one in sydney, and a couple in the whitsundays. The rest have been reverted to straight wheels or broken.
PM me with your credentials and I will offer some advice as to what to do. But a 208 water rating without any float time will be a complete waste of everyones time, and your money. Most operators will endorse you if they want you to fly their one, but simply to buy one with no time afterwards is silly. But don't let me stop you if thats the case. The states is the place to go. You can buy anything there, and Jack Browns Float School is the best for that.
