Quite a few restaurants in the Nagoya area serve up authentic Thai food, or ingredients. Thai food gets more popular every year in Japan, and you can bet there are more options than these out there, but none as popular with the foreign communities of Nagoya. Here we have three options for your perusal: 2 restaurants and a grocery store.
Another nice place to eat is Siam Garden, which is near the Hilton in Fushimi. The building is the coolest part about that location. I heard once that it used to be a Thai consulate many years ago, but it really looks like an old bank.
If a night out on the town is not what you seek, but the means to cook Thai food yourself then you will want to know about the small Thai grocery near Sakae. Chaiyaphum is very small, but it is the only place I have found where you can get Thai basil reliably. It’s a bit of a walk, but its worth it if you are in the market for Thai ingredients. The owner is Thai, and they do not speak any English, but they are very nice so stop in anyway!