Can anyone suggest about the external power of the servo motors?
I have a hose. Can you tell me how long it will take to fill my bucket. I won't tell you what size hose, what the water pressure is, or how big my bucket is, but I want you tell me how long it will take to fill the bucket.
Pretty hard, isn't it. You've told us nothing about your servo. How much current does it draw? What voltage is it? What duty cycle will you be expecting? What load is the servo moving? How fast?
There are so many things that you haven't told us that even a guess as to the external power requirements would be impossible. All we can say now is that you need some.