They seem to be cracking down on non tourists sims, and require a thai national card to buy them.
But I just went to a dtac/true store ask them for the 50baht esim (they will try selling you tourist packages just say no just esim only) it comes with 1 day unlimited then install the app and you will have heaps of packages to pick from all allot cheaper than the tourist package.
I got the 450 baht unlimited 10mbs data for 30days