I think you’ll struggle to source it in Bangkok.
I’m in Issan and make cheese from raw cows milk. I sourced mine in the following.
I trawled the internet for cow and goat farms in my area without success.
I then the visited the local government agriculture office who gave me 2 leads.
List of of local Veterinarians and Milk Cooperatives ( collecting sites for Raw milk from farms )
The Vet was helpful but only for the sale of goats.
The Milk Cooperatives (cows) came up trumps. They could not sell any but gave me the details of a couple of farms nearby.
Went to the nearest one some 10km and purchased 5 litres B150. Happy to sell for cash.
As you are in Bangkok I appreciate that it will be a bit more difficult but with some digging and if you are prepared to travel some you should be able to source.
Good luck.