This question has come up a couple of times in the list of search engine terms that have led to my blog. I haven’t answered the question directly in any of my postings so far (except in the now-defunct ‘Q&A’ page), so I’ll put it up here now.
Firstly, try the Japanese department stores – Takashimaya has the best range of Japanese cookware, also try Isetan.
Daiso definitely stocks them too, and at only S$2 (no guarantees on quality though!).
Another possible place to look for them is in specialist professional cookware shops like Sia Huat in Temple Street.