Can you design a simple poster asking for models for inexpensive cuts/colours etc. and put copies up locally? Explain that all work is fully supervised and using professional products.
Try your local community centre, pub/club, gym. etc.
Also, try to swap clients with other students so you do your Aunty Brenda one week and another student gives her a cut 6 weeks later. Then she gives her mum some highlights and you do her mum's colour another time. That way you can both pass an assessment using the same client.