Hard fish to find. Most likely you will need to find a person who wants to sell the one(s) they have had already.
Unless you find a connection who knows some smugglers.
If you're in Singapore then I shouldn't have thought you'd have much trouble, the only issue is price and whether you'll pay it. If you haven't already try Neo Kim Suey Aquarium, C328 at Clemente and Stones Aquarium, I'm sure there are many more you can try but these are the ones I know of.
Try Arofanatics.com and PlecoclubSingapore.com as they have active classifieds forums.