Oh dear.. Sorry to hear that but hope that you'll enjoy your purchases eventually and not purely for the quota. Frankly I love my purchases more when I started wearing them than when I first bought it as they are very versatile and of good quality. Do understand the frustration when everything is not available. Not sure what you've requested for, like others have mentioned, it could be too popular and depends on the fastest fingers, plus, stocks seem really really low since the end of last year.
I started out visiting quite frequently (Every few weeks) to make purchases, glad that during that time (early last year) I'm still able to get things that I like. Sometimes, I asked for things and manage to see them in store myself before my SA even update me (or will I be prompted?) but there were also times she'll update and keep it aside for me. So it's give and take and I conclude that they are really really busy and might have overlook or for whatever reason. It may be easier to register interest for items that is yet to launch, arrive in SG. Just try to be more pro-active and thick skin ourselves but not too overly else it'll be annoying already. Yea.. this game can be quite frustrating sometimes. I hope you get your QB soon and by then you can decide whether or not to switch store.