Tough one. I sometimes get souvenirs from HK Disney (which has a shop at the airport) or Oceanworld.

Normally, I pick up my souvenirs from other areas. There's nothing really indigenous to Hong Kong. Only other suggestion are the boutique shops in the duty-free area of HKG airport. I was told that, because it's owned by the duty-free shop and not the brand, they are are free to give higher discounts than outside. I've bought quite a few items there.