Gypsum cast up & retainer making

Afternoon

I currently work in an orthodontic practise and the nurses in our practise cast up gypsum models and make retainers in house using earth stone and a vaccum lamp, the current nurses were trained in house but unfortunatley the lady that orginally provided the training has now left the practise and I'm struggerling to find a similar corse/training programme to help me achieve this also.
Please does anyone know anyone or anywhere that provdies this kind of training.
Many Thanks
Fiona