Is there a way to get the original data used to create performance charts? I want to create a flight planning software for GA. Just as a prototype for the time being. The performance data and info about the planes should be stored in various databases. 

When I go through flight manuals like the CESSNA 150, I get a lot of tables which I could convert into a database, but where do I get data which created these charts e.g. the range profiles?

Is this data available somewhere? Or are there databases available to be used?
As others have stated, the data certainly exists but the manufacturers are under no obligation to provide anything more than what's in the manual.  

That said, the performance equations are straightforward and with some effort you could build the tables.  What you are proposing exists for most air transport aircraft for their Flight Management Systems.  

As a reference, you might check out Getting to Grips with Aircraft Performance.  It's written by Airbus but provides a very good explanation including much of the math.