I want to get and improve the source of the
LaTeX2HTML program, but the top Google results are outdated, with broken links.
Does anyone know where the source resides?
There is no single place to get the source as there is no definitive version of the application.
In addition to Peter's answer on the source code on CTAN, other places have different versions. This arises as distributors may have the project marked as 'not part of an upstream project', i.e. there is no single place to send copies of downstream changes as there is no known active maintainer. For example, Ubuntu regards the package in this way.
As a result there may be differences in the package and the source code depending where you obtain them from. The version history for Ubuntu shows that changes have been promulgated via Debian later than 2008. The current Ubuntu source and patch file are available to download.
As a result you may find that you have more than one version of the executable available and will need to look at the correct source code package.
On my system, Ubuntu 11.04 but with a full Tex Live 2011 installation,
I would think the source would be at