Well, you'll need to ensure the GROUND / 0V are all common
Then possibly break the servos into groups (so the power supply isn't huge).
Let's agree we are talking about RC style servos.. !
Say... each group of six servos is connected to a *single power supply, while the control wire still goes back to the Arduino servo control pins.
- the rating of each cluster power supply depends on the type of servos, and the current requirement (mA or A) for the cluster of (six) servos.
e.g. 6 servos x 1.5A = 9A supply
or 6 servos x 500mA = 3A supply
Note that servos can draw MORE power if they are under load or 'stalled'.