Don't have an orchestra handy? Think again.
What about using iPads? - If you can round up half a dozen, there are many instrument apps available and there are many fun things being done in both composition and performance using these devices. (or even as a supplement to existing band instruments.)
iPad apps in action
https://www.youtube.com/watch?v=aSC2QS1VOZo <- this one is great!
Take a look at "Rockmate" too.