Alternatively, which months is production at its peak?

With such a difference between weather from far north to south, with availability of water being a factor and with growing under plastic in some places, there is likely to be little change year round if you are buying from a supermarket. 

Based on my own experience growing toms in Isan (small scale, non-commercial), the best time of year for tomatoes is the cold/cool season. 

However, with protection from the scorching sun and the pouring rain during the rest of the year it is possible to grow tomatoes all year round. 

Most producers usually want to know when prices are highest, not lowest.

 

I believe tomato prices are highest in the wet season and then tomato plants are  best grown under plastic roofs to protect them from the rain that causes diseases.  

 

Furthermore, in the dry season, tomatoes can be grown in irrigated rice paddy land that is often available in the dry season but not in the wet season (when it is planted with maincrop rice)

 

I am sure there other members here who know better than I do. I hope they chip in.