I have three treasured Japanese knives which I prefer to let someone else sharpen.
After quite a bit of searching I found these people in Outram who I can thoroughly recommend
RAZORSHARP PTE LTD
315 Outram Road #01-03,
Tan Boon Liat Building,
Singapore 169074.
http://www.razorsharp.com.sg/contact.html
I don't know if they collect/deliver and they quoted 2 - 3 days turnaround (actually two). Price was $18 SGD for a 7" blade and I was reassured by their knowledge of steel types and blade angles. They did a good job (including oiling the handles), made sure I was happy and offered advice before asking for my hard-earned.
I noticed they sell Wusthoff knives too.
hth