Wow Pimm's fan you get about. I don't think I'll be going out of the country before next Easter though so this is not an option for me at the moment. The bottles are heavy so I don't like to ask visitors to bring them. If they offer to bring something from home I ask for tea bags. Much lighter and won't break if in hold luggage.
If I were you I'd ask at one of those specialist booze shops. There's one in Changi village (I can't remember the name, it's a woman's name but not Denise wine shops - Sally or maggie or something). That's the kind of shop which would, I'm sure be able to tell you if they could order it in for you. Other than that, you could try the posh cold storages if you haven't tried them already - Jasons and Market place. Or maybe Carrefour
