Sorry this is a bit sketchy, it's been a while since I did it..
I designed a large (1.7m * 0.9m) exhibition display about a year ago.
The company printed it on a wide format (1.2m wide) printer onto thin vinyl then pasted it onto flexible 2-3mm board. (Some sort of plastic material.)
You might look at getting it done at a similar place. It was relatively cheap (£160 for the entire thing, printed in two pieces 0.85m wide), and the company was extremely flexible on sizes/etc. And of course because it's relatively thing, it's easy to bend!
Good thing is, because they're designed for exhibitions they use good quality non-shiny materials that can be viewed nicely under harsh lighting at wide angle, and also within safety regulations (at least in the UK).
I can dig out more info if required. Hope that's some use..
Are we talking photograph or art?? Where I work, we do artwork (decorative painting) on canvas to fit any size room or architecture and then it is glued into place, or is glued to flexible board and put into place with small nails if it is a piece that will need to be moved.
Check companies which make signage. I'm pretty sure I've seen large-format inkjets set up to print on thick but flexible plastic sheeting, including some which can be backlit.
