Fair enough. Despite your aversion to the 'print it smaller and piece it together' idea, you may want to look at places that print designs onto wallpaper. You still have to piece it together yourself but it will come cut to the right size and properly aligned, and be a lot more manageable to put up without creasing or tearing than a single huge sheet.

Try
http://www.designyourwall.com
http://www.conceptcoverings.co.uk
http://www.wallpapermurals.co.uk