21104 NASA Mars Curiosity Rover?
Gev already answered the question about availability. LEGO Ideas sets are produced in small quantities. Perhaps this will change in the future as LEGO Ideas is now out of beta testing and was brought in-house by LEGO. The Curiosity is not going to be back unfortunately. I just called LEGO about this a couple of days ago.

As far as the Curiosity inventory, BrickLink has the full parts-list here: http://www.bricklink.com/catalogItemInv.asp?S=21104-1. None of the parts are rare or difficult to find. You can use the parts-list linked above, add them to your wanted list on BrickLink, then quiry your wanted list by shop. This will show you which stores have all the parts you need in stock. And you can download the building instructions from LEGO's customer service website here: http://service.lego.com/en-us/buildinginstructions/