I really cant imagine there is any tailor shop in Thailand that has experience with tartan or kilts as there must be practically no demand. If you were to take your own tartan, kilt and instructions then I'm sure you will find a tailor that can copy your kilt. But would I risk it?

If you wanted a kilt made out of suit type material or thicker then I'm sure they will be willing to accommodate you but its a humid country where there is little demand for thicker cloths.

Of course I could be completely wrong but I didnt see anything like that when I've been in Bangkok.