Update. I picked up 12 liters today at Kawasaki on Rama 9. Thanks again Tony. Luckily one of my bikes is a D-tracker, so they agreed to sell me the oil. They actually checked to make sure I was in their system. Strange, but I guess it is just one of those Thai things that makes you scratch your head.
Checked some places near my house (Red Barron, Shell Station, another Kawasaki big bike dealer on Ramkhamhaeng) for future reference but no luck.
Next time at the Ducati dealership I will talk to Jay and ask him for some more suppliers. I sure he must know.