Building MacOS 10.8 source code on 10.6

I have Mac OS 10.6
SparkleShare claims to run on Snow Leopard (10.6) or later
SparkleShare contains calls to NSUserNotification, a class which is Available in OS X v10.8 and later

Monodevelop throws an error:

error CS0246: The type or namespace name `NSUserNotification' could not be found. Are you missing a using directive or an assembly reference?

In Monodevelop, when I begin typing MonoMac.Foundation.NSUser, the only suggested item is NSUserDefaults, NSUserNotification is not suggested.

Is this kind of cross-compilation possible?
I can't upgrade to 10.8 because I also want to check how the user experience is on 10.6.

Solution

Run:

git clone https://github.com/mono/monomac
git clone https://github.com/mono/maccore
cd monomac
make

It should generate MonoMac.dll. Copy it to wherever your MonoMac.dll is, restart Monodevelop, the project should now build fine.