Where can I find data on past forecasts of planned aircraft production? Does anyone know of a database which would list the expected production rates for various aircraft, at the time those aircraft started production?

Finding actual production to date is easy, but I would be interested in what was the original planned production. I am not interested in current forecasts, I am interested in past forecasts that have been made before or at the start of production for the particular aircraft.

E.g. Cessna 152 was assumed by the manufacturer to be sold at the volume of XX aircraft per year, when the production plan was put into place.
Yes both Airbus and Boeing deliver 20-year forecast for the complete market. For Airbus there is a spreadsheet which may function as your database.

IATA also publishes 20 year travel forecasts, here is the latest. Airline travel is going to double over the next 20 years.

At he time of first production, forecasts for the aircraft are made based on market forecasts, plus the expected market share that the aircraft may achieve. Information that is of interest to the stakeholders of the company.