A Supportive industrial city can provide all the "dirty" tokens for your main, clean city. The problem is that all of your employees in the industrial city need to live there.
It is best to specialize in Heavy Industry, Manufacturing Industry, and either Fuel, Electricity, or Waste Treatment since one can usually only get all the bonus buildings for up to 3 tokens per city.
Gallery of example city[]
An industrial district separated from an unskilled workers' district by a park
Industrial district with fuel, power, and waste