Other than sending one's lenses to the respective service centers (Canon, Nikon, Sony etc), there're a few locations where one can get their lenses cleaned.

Do add on the following if you've found any!

The Camera Consultant - Philip Tay
511 Guillemard Road
#01-46 Grandlink Square
Singapore 399849
T: +65-6742-6383
E: enquiries@decameraconsultant.com
http://www.decameraconsultant.com/decamera/web/

The Camera Hospital
91 Bencoolen Street
#01-67 Sunshine Plaza
Singapore 189652
Tel: +65-63360025
http://camerahospital.com/

Alexfoto
111 North Bridge Rd #02-40 Singapore 179098
Tel : +65-63340998