You shouldn't have any problem getting things especially so close to Singapore, most of this stuff is made in this area of the world so really everyone else is on the other side of the world in that regard. I have no problem finding things in Northern Thailand and I would say that is more "isolated" than Singapore.
http://www.lazada.co.id/power-supply-silverstone-sst-st45sf-g-5807242.html - Lazada Indonesia has it listed and from what I can see at a decent price.
http://www.lazada.sg/silverstone-sfx-450w-80plus-gold-229211.html - Lazada Singapore has a great selection of SilverStone stuff as well if they will ship to you or you can ship to someone in Singapore and pick it up on a trip there.
I can vouch for this, it doesn't get much worse than New Zealand... so if New Zealand has them you can probably pick them up from a street vendor in Mongolia.
Thanks Mr. Michael for making it easier for me! I decide that SFX PSU is indeed the way to go with my future build; I might want to find some potential buyers to my older components before that.