Visit a spray foam business in your area and ask if they will be holding any closed-cell training courses in the future. If they aren't ask, if you can pay a technician for a one-on-one training session.
Visit a college's engineering and construction department in your area. Some departments hold spray foam tutorials throughout the school year for the general public.
Contact national foam insulation associations, such as the Spray Polyurethane Foam Alliance, and ask if they are holding or can hold closed-cell information sessions in your area.
Navigate to foam insulation websites, such as Insulation Contractors Association of America or Sprayfoam Distributors of New England, to get training information.
Read foam insulation books, such as "The Solar House: Passive Heating and Cooling" by Daniel Chiras, and articles about closed-cell foam insulation, such as those found in Spray Foam magazine.