Heh, good to see people think it's an official or authorized expansion. Shows our focus on quality is paying off.
Answering the question, you'll never be able to
buy Machina Terra. It is a fan project, and hence it's unnofficial and will be distributted
free of charge when it's done. We're working on it as fast as we can, but since we can only dedicate our free time to it, sometimes development gets real slow.
I was hoping to have it done still this year, but some events on Real Life are preventing me from dedicating all time I wanted to the project, so I can't say for sure when it'll be done. If things settle down quickly, I hope for it to be released on the first months of the next year...
Keep checking this place and the website for updates...