What is the comprehensive methodology for identifying potential stakeholder for a project?

I would go about 1. understanding who are the key decision makers

2. who own or influence resources that are needed for the project

3. who are directly and indirectly impacted

I will then plot a 2*2 matrix with X-axis listing stakeholder based on power they yield

and Y-axis listing their interest or support level...stakeholder with high power and low support will be the bottom right hand corner and you will have to think of a strategy to turn them around. Similarly the top right corner box will have stakeholder with high power and high interest and they can become your champions.