getting read-only data from object

I have a database-like object that looks like:

static class Data
{ 
     private Dictionary<String,Car> cars;
}

class Car
{
     private string name;
     private Dictionary<String,Part> parts;
}
class Part
{
     private string name;
     private double paramA;
     private int paramB;
     private string paramC;
}

I use this database in a multi-core program, so i only read from it. Currently, reading is implemented thusly: in Data I have:

public double get_paramA(string car,string part)
{
     return cars[car].get_paramA(part);
}

and in Car I have:

public double get_paramA(string part)
{
     return Part[part].get_paramA();
}

This works, but i am worried about the future if there is a need to add more params to Part: in the current scheme it adds 3 functions to three objects.

How should i change the reading-scheme to make the code more readable/maintainable?

Sorry if this is a standard question, i have no idea what to search for to find an answer.