you can pickup any 5 stud spare wheels. I have one from an old A4, one of those 50mph Max skinny spare. They fit where the space saver should go. When I had a puncture at the front, I took the rear wheel out and put it at the front, then let the rear have the spare wheel. This works well, although a little bit more work.
I haven't bothered to get the mounting bracket tho, so I tie the spare down using the hooks for the cargo net and it doesn't roll from side to side in the boot But if anyone know how much it is for the bracket and the bolt to secure the space saver, I'll be interested. I'm sure it is compatible.