You should be able to find them at some supermarkets in and around town, and definitely at the old Hua-Hin shopping mall just up from the clock tower.
@HHTel........yes, a loofah is plant, also commonly known as a sponge gourd. The fruits are typically eaten, but can also be left to fully mature and then be used for making the sort of scrubbers mentioned in the OP.

Don't try to impress me with your manner of dress cos a monkey himself is a monkey no less - cold fact