I couldn't find this as well ( i viewed a demo of the book that contained the chapter and it doesn't say more then what you are telling).
So i searched around and found the code for monocross on google code and checked out the trunk using svn.
There i learned that they only have finished the templates for the android side of things (!)
By opening the Monodevelop app content on my MBP.
All that's left after that is copying the
trunk/MonoCross.Templates.MonoDevelop/MonoDevelop.MonoCross
subdir and all its contents into the mac app bundle under
Contents/MacOS/lib/monodevelop/Addins
and restart MonoDevelop.
After that you can see Monocross category under the C# section with (merely) the Android templates.
I hope this helps & brings to attention that they are not there yet...