HMV. But they're real pricey, being imports.
I always buy my CDs online. Some online anime stores based in
Singapore don't list CDs on their websites, but they may have it in
places like eBay, so perhaps you'd like to check out eBay
Singapore.
The cheapest I bought was the Last Exile soundtrack by Dolce
Triade, at SGD20.00 for both Soundtrack 1 and 2. They were probably
parallel imports, because the CD booklet printing quality was quite
inferior. I think it was from Taiwan. And I found it on eBay
Singapore. 
