Tried already, and failed. Neither Amazon.ca or .com has it in stock (and actually I just spent all the money I had for books at the moment, so the library is going to be key for the next little while). Thanks for the links, though, as well as the name Jack Williamson.Get The Past Through Tomorrow by Heinlein-it includes Green Hills, as well as the rest of his Future History. And you might look into Jack Williamson as well.
You might have to track a used bookstore for the Heinlein-I bought mine a long time ago. Here's where I go.
http://www.littleoldbookshop.com/
The owner's name is Brett and he's a really cool dude. You might want to drop him a line.