tbh, there isnt many shop selling this kind of equipment here.
You could try Ruby Photo, where they have a bunch of developing chemicals, 4x5 papers, some 35mm film and paterson tanks. (Cathay Photo, in the opposite block facing the building, might have what you're looking for.) A walk in the area would yield a few more camera shops.
Ruby Photo, at Peninsula Shopping Complex --> Peninsula Shopping Complex / 3 Coleman Street, Peninsula Shopping Centre, Singapore 179804 / +65 6336 8610 ?