The 'common' banana available in Thailand is neither Gros Michel nor Cavendish. It's a tiny little thing that (going by a photo on Wikipedia it's something similar to a Latundan I believe) IMO is only useful for blending (i.e. for a smoothy) because it's too 'moist' to eat as-is. Thai's seem to mostly grill or fry them, rather than eating them fresh.
We recently (this year) have been able to grow the less common (and more expensive to buy locally) 'big' bananas, which I've confirmed today are in fact cavendish.
I'll ask my in-laws (who had already grown Cavendish) if they know anything about where to buy/find either Gros Michel fruit, or plants.
This whole thing gets quite confusing (for me at least) as I don't read (and speak very little) Thai, and software translators convert the Thai for "Banana", "Cavendish Banana" and "Gros Michel Banana" all into "Banana" in English.
In Kerala (state in South India), you get this variety called Nendran. It is larger than the common variety you get in India, (not sure if the common ones in India are Cavendish or not), and damned tasty. I specifically say tasty, not sweet, because a) it has a unique and good flavor, and b) it is not too sweet. People often boil it and eat it, which is not done with the common variety. I just googled a bit for it but cannot find its English or Latin name, but did find this:
which has Nendran as a cultivar under the Plantains category. But the Wikipedia link for it redirects to the main link for Banana. But that link does have a photo of it:
Anyone visiting Kerala, consider asking for it and trying it out.
Edit: The cultivars list above has Nendran under the AAB Group - Triploid cultivars of Musa × paradisiaca and within that, under the plantain subgroup.
So that may be the Latin or scientific name, and I guess it is a plantain.
I've been curious to try a Gros Michel too. I read somewhere that they taste much more like artificial banana flavor than the Cavendish do, which dampens my enthusiasm.
Enjoy the Cavendish while you can, a new blight has evolved that is destroying them and spreading worldwide.
We got stuck with Cavendish after a blight hit the monoculture[0]
0. https://en.wikipedia.org/wiki/Cavendish_banana