Hi Roo. You might get more responses to your question if you posted it in the general and cognitive therapy forums.

From an ethical POV, Dr Reid already said it. To use tapes of your actual sessions you need your client's written consent. I would also check with your university to see if they have any additional restrictions.

For commercial videotapes I'd suggest checking out agencies and/or sites that specialize in psych professional resources like APA, the Academy of Cognitive Therapy, Guilford Press, etc.

Good luck on your endeavours.