An update on Singapore. I had the chance to look around today. Forget about Toys R Us - they do stock a range of Tomica cars and sets but no Plarail that I could find.
I did however find a little independent shop called Let's Play. He is located in Sunshine Plaza at 91 Belcoolen St. The guy is really helpful and friendly and has a lot of stuff crammed in all over the place. Recommend checking it out if you find yourself in this neck of the woods.
Here are some pics:



