It is very hard to obtain supplies in SG and also can be very risky. I would introduce yourself in the SG forum (it's under the international forums) and see if you can get any help. Do keep in mind that their "authorities" are monitoring the SG forum, in the hopes of finding vapers that they prosecute, so proceed with caution, and be aware that posting on that forum alone may cause a certain degree of scrutiny so I wouldn't introduce yourself and just ask for suppliers.
It may be a long labyrinthine (expensive and dangerous) endeavor, so stay safe and just introduce yourself there (there is a list of rules for posting, I would read that list and memorize it.) SG is one of the most restrictive countries in regards to vaping, confiscations, legal issues, and huge fines may be levied if caught.
I don't say this to discourage you from vaping (and now I see, your post was in the SG forum) but to make you aware of the dangers involved, which are very very real.
Best of luck,
Anna