Up for sale here is this used Harman-Kardon 730 metal heat-sink.  This is in great shape and will work well for you.  This listing is only for the heat-sink--the amplifier board, outputs, and output sockets are not included.  Please see my pictures for details.

US shipping and handling is $12, and international is $36.  If you have any questions, please ask.

I have more Harman-Kardon parts and other vintage electronics listed--feel free to take a look!