I'm more than certain there must be one or two naturals. Dreams are just one of those things people rarely talk about.

Put up a notice on a school messageboard looking for lucid dreamers, make an announcement over the intercom or look for people on facebook, etc.

Also, I suggest you give your guinea-pigs some sort of tasks to accomplish. First would obviously be performing a reality check to confirm lucidity (just to get it into their heads how they work and to get them into the habit) and simple things such as flight, moving onto more complex procedures such as teleportation and summoning and dream incubation.

You could split the group into ones attempting just regular DILDs as part of their normal sleep cycle, others could try the WBTB technique and compare their success.