I'm looking in the following locations; Hong Kong, Singapore, Malaysia and/or Japan. I really can't find any here in Manila and I want to avoid buying online.

Footlocker or footaction.

Well most sports shops will have them. If you want a very good one it is best to buy online. However you dont really need a scrum cap for rugby, as I dont like playing with one I never wear one, and I am in the scrum.