Contact a manufacturer of lip balm, inform them of what you need and why, and then ask them if they can donate 'x' number of tubes to you.
If you don't have time to do that, I suggest you start asking your friends to save their empty or near-empty tubes or tack up a flyer asking people to give you their old tubes.
Failing that, go to the nearest flea market or dollar store and buy as many tubes as you'll need, as cheaply as possible.
Good luck.