Like the good Panasonic lenses, almost impossible to find in Singapore, it's ridiculous. This is where one can bite the bullet and order online. Just treat the higher cost as fee for being able to get it asap, and delivered to your door without you leaving your house.
Reminds me of some folks who are willing to pay more than the retail price for a Leica M9 at a shop here just to be able to have it.
the big stores like Yodobashi and Bic camera will only offer retail prices + 5% discount for tourists. if you will be in Tokyo and have time, check out the smaller camera stores in Shinjuku as they may have their own in-house promotions for selected brands and items.
i got my GF1 + 20mm pancake kit in Shinjuku for S$1196 during a public holiday promotion at a store in Shinjuku. japanese domestic set but its not a issue for me, came with the leather half case too. there was a canon promotion at that store too, 15% on all canon products. so its worth checking out the smaller stores if you will be there.