Please contact Sajjad Foroughi- s.foroughi@imperial.ac.uk - for a copy of the network extraction code by Dong and Blunt (2009).
A newer version, used as a base for the generalized network extraction code by Raeini, Bijeljic and Blunt (2017), is available on GitHub:
https://github.com/ImperialCollegeLondon/pnextract
You can also use the standalone Windows-based software developed here to perform network extraction effortlessly. This software is built upon the pnextract code.