Gaming- How Does One Source For Supplier?

Hi all, I'm new here, not sure if I have posted my thread in the correct section or not. But there is this one matter has been bugging me all along. If possible, hope some can give me the answers to it.

Anyway, I am from singapore, and I have been seeing alot of online shops opening up one after another. Then sometimes, the pre-orders of certain games which i thought it will be very expensive, some of the online store I have seen, they can sell unexpectedly low. A price that never come across your mind, or that some shops they really do sells the game much more cheaper than other shops of the same reputations.

So my question is, just how do one source for such supplier? I am interested to open up one such store but I had no idea how this supplier stuff works. So will it means that I will have to travel overseas in order to get supplier that is able to at cheaper pricing?