Kian Weng in Air Itam again, but they mostly stock very common water plants. Just be sure that they ARE water plants first b4 u get them.... Too often in malaysia, they sell terrestrial plants as water plants and the plants just rot away and die and cause more problems with the water quality.

In KL, there is AI (Aquatics international, in Subang.. after the old international airport going towards Sungei Buloh.). Apparently there is an aquarium shop in Seremban where the owner specialises in aquarium plants. His shop doesn't really sell lots of plants (Water plants aren't popular in Malaysia... too much work to keep them... High intensity lighting, CO2 system, fertiliser.... Most ppl just can't be bothered.), but he has a whole farm producing just water plants for export.

I'm presuming you know what you're doing with the plants... because if you don't, they're not as easy as just putting them in the water and they will grow.