I live in Singapore, which has had LEGO Certified Stores since 2014. Like LEGO Brand Stores overseas, they feature Pick A Brick walls with selections of LEGO elements that can be purchased using large or small Pick A Brick cups. These selections change over time as stocks of one element run out and it gets replaced with a random other element.
As I've been visiting local LEGO Certified Stores every now and then since 2018, I've started this resource to keep track of the Pick A Brick inventory at each store. Things to keep in mind:
Neither LEGO Singapore nor any of these stores is responsible for the information you see here. The information is presented solely by me, on a voluntary basis, and I don't work for LEGO or at any of these stores.
As of August 2018, Bricks World has launched a Facebook Messenger service that tells you which, if any, of their stores has a certain part and/or color you're looking for, and is updated each day. You can find it here. This is an official service that is unrelated to my site and I did not work on!
I patronize some stores more than others at my own convenience, so the information is not always and consistently up to date, by design.
I don't have a way for you to suggest inventory updates just yet, but feel free to contact me if something's changed at a store recently!