The functionality has been added to octokit.net recently:
https://github.com/octokit/octokit.net/blob/b07ce6e11a1b286dda0a65ee427bda3b8abcefb8/Octokit.Reactive/Clients/ObservableRepositoryForksClient.cs#L31
/// <summary>
/// Gets the list of forks defined for a repository
/// </summary>
/// <remarks>
/// See <a href="http://developer.github.com/v3/repos/forks/#list-forks">API documentation</a> for more information.
/// </remarks>
/// <param name="owner">The owner of the repository</param>
/// <param name="name">The name of the repository</param>
public IObservable<Repository> GetAll(string owner, string name)
{
Ensure.ArgumentNotNullOrEmptyString(owner, "owner");
Ensure.ArgumentNotNullOrEmptyString(name, "name");
return GetAll(owner, name, ApiOptions.None);
}
Similar functions exist for other ways to specify repository.
Please feel free to edit in the full code for this use case here.