The reason you could not find the keyframes is because there aren't any!
See when you use the Follow Path command blender sets up the curve animation by using a generator. You can see this generator by opening up the properties panel in the graph editor, with the curve selected.
That is not what you want. You need just two regular keyframes. So delete that modifier (just click the X).
Now you can keyframe the curve Evaluation Time. Go to the first frame, set the Evaluation Time to 0 hover over the input field, and press
Now go to frame 100 and set the evaluation time to 100, again hover over the input field, and press
Now in the graph editor you will see your animation (if the curve is still selected). You can drag out the ending keyframe to make the whole animation last longer (camera spin slower), but what you are really interested in is changing the curve. (By default the interpolation type is Bezier and that is what you want.)
With the generator you were getting a linear animation, with the bezier interpolated keyframes you have a nice easing at either end.