First of all, in December we released a new tool called Objective Sharpie that can automatically bind Objective-C libraries into C#:
http://forums.xamarin.com/categories/ObjectiveSharpie
If you're skilled enough to build the Objective-C library, then you'll be able to use Objective Sharpie to create a C# binding. We also have docs on doing this for Java on developer.xamarin.com.
Some of our customers don't have the time or skill to do this themselves, and so we've recently created a bindings team that wraps third-party native libraries for our customers. Many of these end up published on http://components.xamarin.com/ (there are over 300 components now). But some of them we can't immediately publish because we need to get permission from the original library author to redistribute their library. This is especially true for commercial SDKs. But if you contact us directly, we might be able to give you something.
We also do custom bindings through our support team. This is something that unfortunately we haven't made very obvious. But you can just email support@xamarin.com and we can create a binding for you.
Like I said, this is an area we're pretty focused on. If you have any feedback, please feel free to let me know directly: nat@xamarin.com.