Can I not buy it out of season?
It is listed as Main season Apr–Aug. It is available all year round, but quantity and price can change with the season and variety. The calendar does not guarantee that the fruit is on sale on any given day.
Durian · ทุเรียน
If its strong smell has made you hesitate, you can still try just a little durian. Inside the thorny rind is rich, yellow flesh. You taste the smooth, sweet flesh and its aroma together in one bite. If it is your first time, start at a place that sells a small amount of flesh rather than buying a whole fruit.

Main season Apr–Aug
Listed as available all year round
Durian of the Sisaket volcanic area: season listed as May–Jun
Use the main season, or the season of a regional fruit, as a guide. Actual availability can vary with growing area, variety and weather.
Its character is a sweet, rich taste and creamy flesh. The firmness and smell of the flesh differ with variety, such as Monthong and Chanee, and with ripeness.
Thai durian varieties such as Monthong, Chanee and Kan Yao are well known. Because of its strong smell and sweet, rich flesh, it is also a fruit on which tastes divide sharply. You can eat it as it is, or enjoy it in ice cream and desserts.
It is listed as Main season Apr–Aug. It is available all year round, but quantity and price can change with the season and variety. The calendar does not guarantee that the fruit is on sale on any given day.
First ask whether the price tag is per kg of whole fruit including the rind or per kg of prepared flesh. If you want to take it to a hotel or on transport, it is better to check the rules on bringing it in first.
If you want to read more about these dishes and regions, these sources are a good place to start. Ingredients and cooking methods can differ from one eatery to another.
Sharing image credit: مانفی · CC BY-SA 4.0