There are two places that you can experience the red lotus like the one I use for cooking: Bueng Boraphet and Bueng Nong Harn.
Bueng Boraphet or Boraphet lake is located in Nakhonsawan province, 3 Hrs drive up north from Bangkok. It is the biggest lake in Thailand. Bueng Nong Harn or Nong Harn lake is located in Udonthani province, 1.30 Hrs by plane. Both places have more or less the same kind of lotus that can be cooked.
I have attached links in case you want to know more about the subject.:
Bueng Nong Harn
The meaning of the word
Sai-Bua means lotus stem
Tom means Soup or boil
Ka Ti means Coconut milk
Sai Bua Tom Ka Ti is a dish with lotus stems as the main ingredient. It will be easier to get lotus stems in the rainy season because most lakes fill up with water and lotuses grow better.
When I was a kid, I sometimes went with my family to the lake nearby our house and pulled some lotus stems for cooking. Sai Bua Tom Ka Ti is our house's favourite dish, among others, during the rainy season. What can be better than have hot creamy soup, rich in nutrients, with jasmine rice while it's raining and chilly?