Graham,
Wouldn't it be far easier to pull actual transmissions from various locations? As a bonus you could then ask students to identify improper phraselogy, and then state the correct phraselogy. I'm also sure that some of the guys over at the tower would be happy to help you make some recordings using good phraselogy to help you out with your class.
Remember real life radio transmissions are far better than simulations. In the past that was one of the major complaints about the FAA Academy, you guys didn't train for real world, just the imaginary one, so when students reported to their facilities they weren't prepared for the real world or air traffic control.
Mike
NATCA A80