Hi Blake
We've done a lot of Method API work in the .Net space. As far as I know the only available open source code is provided by Method in their API examples.
We've built our own class library that abstracts away a good bit of the API but we still have to handle specific field mapping for every project.
Our class library is not open source or for sale. Although, we are available to help you or your developers on a consulting basis. Usually that's all that's needed to get you over the hump.