Where can I buy Nystatin (anti-fugal) - either tablet or pure powder suitable internal use. What is approximate costs? And is it marketed under any brand name which will help a pharmacist identify it?

This link gives some brand names:

http://www.nlm.nih.gov/medlineplus/druginfo/meds/a682758.html#brand-name-1

You can also try wikipedia for brandnames.

Nystatin is not available in tablet form in Thailand, just topical form and as an oral suspension meant to be used like a rinse and then spit out (for oral thrush).

I bought Nystatin in BKK in a liquid form, packed in a yellow box, called TYSTA. Not each drugstore has it so have to search a little bit. Not expensive.