Vinegar in 5 liter containers are readily available in Makro, some Lotus's and presumably, Big Cs.
For use, mix with Baking powder, (Sodium Bicarbonate) - available as above and at the Chemical store on the Mahidol Rd, 2/3 Km from Airport Plaza, CM - together with a bit of elbow grease and a scotch bright pad, will remove most stains, scale and bathroom tiles.
We use it extensively and it is exceptionally cheap to buy.