cendrine,
You can get the milk bags in all the dept stores, kiddy palace etc and also online, like Qoo10 and other baby online shops. There are many brands. There are also mummies selling extras on the want to sell forum. If you know anyone going bkk, you can also get the one from Boots pharmacy; that one is cheap compared to singapore prices.
viiv,
I didn't respond very well to pumps, so definitely not an expert. Prefer to latch directly actually. No cleaning up, no need to pump, no sterilising, no need to lug bottles, hot water and ice bag around,no screaming baby while waiting for milk to warm up. Baby want milk, just whip it out and everyone happy

anytime anywhere. So convenient
For some reason medela works best for me. I have tried the Ameda Lactaline, Avent manual, Medela PISA, Medela Harmony and the Medela freestyle. I will be standing by my harmony during ML to pump more for #1(though it won't be necessary if she decides she want to latch again) and looking around for a freestyle when I get back to work. The PISA works for me too; but I find it a little rough, heavy and many parts to wash. There are some mummies who find that PISA works better for them than freestyle also.
I have friends who exclusively pump with the medela harmony and the avent manual without problems. Another friend on the Ameda Lactaline who pumps really well with that. So like I said it's a personal thing.