The NMock source code is hosted by SourceForge inside a CVS repository. To check out the source, follow the instructions on the SourceForge CVS page. You can also browse the code online using the CVS browser. The NMock source code is in the nmock CVS module, the NMock 2.0 source is in the nmock2 module.
We encourage everyone to use Tortoise CVS as their client—it integrates nicely into Windows Explorer and allows you to create and apply patch files easily.
We continuously build NMock using CruiseControl.NET. To see the current build status, check out the CCNet Live build page. To download a recent build, try the builds directory, but bear in mind that these are bleeding edge builds and not official releases.