Not really.
The buoys are not owned by Thailand. They do not pay for them. They are only responsible for checking the operation of the buoys. The costs and availability of these buoys (which are tethered to the ocean floor) is prohibitive for stockpiling spares.
Also there other ocean systems scattered around the world, so in a way there is redundancy and overlap for very accurate Tsunami prediction in all oceans, but as I outline below they are not the first line of defence.
Also something you may not know...Tsunami buoys are not the first systems used for Tsunami prediction...Thousands of Earthquake Monitoring Stations around the world measure the intensity of earthquakes, and using computor modelling from many many years of data, the likelyhood of a Tsunami generating (and its probable direction and strength) is plotted quite quickly. Data from any ocean buoys can then be used to calculate the velocity/height/timing of the generated waves for the affected area.