Hi Wimbeldon,
I have had to deal with this problem many times. Here are the local resources I have had some luck with:
Yes Robinsons has a small winter section, even smaller now that its summer I'm afraid. Not great but worth a try.
Export Fashions (HV, Tanglin Mall, etc...) may have a few pieces as well as the place around the corner at Holland Village near Coffee Bean and Sasa. I got a J Crew down vest there the day before a surprise trip to the Blue Mountains. Look in the back of the store.
Winter Wear at Plaza Singpura (also at the same mall as Fugi Ice Palace, but not really worth the trip).
Better still, if you have the time for shipping:
www.landsend.com
www.llbean.com
Both deliver to Singapore, both have a good selection of cold weather items all year.
Remember -- it's all about layering...
