Just moved into a new place which I like but the clear plastic door on the freezer section of the refrigerator is missing. Does anyone know where in Bangkok I could go to buy this part which should be available ?

I seriously doubt it would be available in Thailand outside order by Samsung Service Center (you can find them with Google).  Thailand has very few sources for spare parts as most do not DIY and know our repair of Samsung unit required order of parts from Singapore (and they were much more common failure items).  Alternative might be a refrigerator repair store (if you can find one these days) as they might have source for used parts.