There is the 0/3 baby shop in Ocean Terminal, TST. It's worth paying a visit there because they have quite a few shops selling baby things (On the very ground floor) and several shops selling change tables.
IKEA have a very limited selection- just two choices but they are cheap!
Also there is a shop in Windsor House, Causeway Bay- forgot it's name but it's on the same floor as Mothercare- where you can order change tables with baths in but they seem to be around $4-6,000!