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I do not know about Singapore....
But just in case this info is useful for you.......
I remember seeing those slippers in Chennai Kadhi that is near paris corner / poo kadai.
Also about 10 years back, a friend bought those slippers from a guy who sells them regularly to professors in Vaishnava college. A friend told me this info and bought one for me too.
Not sure how useful this is for you.