Access-NL.org
Essential emergency telephone numbers, including lost property offices in Amsterdam. In PDF format.
http://www.access-nl.org/our_services/pdf/useful_numbers.pdf

BUG Europe
Contains information on lost property offices in the city.
http://www.bugeurope.com/amsterdam/info.html

Housing Online.nl
Lost property offices in Amsterdam listed.
http://www.housingonline.nl/pathfinder.asp