I've been a bit frustrated with subversion / TFS source control system, so I have asked the CodePlex team to migrate DiscUtils over to Mercurial.
I hope this will happen in the next few days.
If you currently access the project using a subversion client (such as TortoiseSVN), you'll need to migrate to an equivalent. I've been trying out TortoiseHg, and found it works pretty well. The CodePlex team have posted a blog explaining how
to get started with TortoiseHg:
The details you'll need to access the source code will hopefully appear on the Source Code tab when the migration is done.