I have 6 UNO R3 1 MEGA , motor driver and servo driver - i would like to power these from one source i possible - could anyone suggest what type of equipment I need and where I might get it.
Many thanks in advance -
What voltage(s) do the motor and servo use?
I would use a power supply of the highest voltage of those 2. Then use step down (buck) converter(s) to drop that voltage to 5V to connect to all the Arduino 5V pins.
Avoid using the power jack and Vin. Those inputs go to the onboard 5V regulator. That regulator is weak and can supply limited current before it gets hot and shuts down.
Most everything seems to run on 12v 2 amp it's for a model railway HO scale.
Servos usually run on 4.8 to 6V, and a single servo can consume more than 2 Amperes.
For informed advice, please post links to the exact components and the power supply that you plan to use.
Why so many? In fact, why more than one?
Well to be honest I sort of went down the rabbit hole thinking I needed a few of them and then I sort of inherited some more from someone.
My plan was/is to have the Mega as the master controller using the UNO's as subsystems. Each subsystem will have NRF. (because I have them also).
The controller will have leds, switches, NRF to control the subsystems:
Sub 1:Servos 10 of them 9g MS18 with a PCA9685.
Sub 2:Signals 8 leds for each servo with a switch register output.
74Hc165/74Hv595
Sub 3:Lighting for outbuildings with a switch register output. 74Hv595
Sub 4: Throttle master L298N motor driver and slave (to be remote controlled)
buttons, led Rotary encoder KY-040
Sub 5: Possibly some sensors - if I live that long.
So you can see that power will at some point be a problem for me - hence I would like to know what will be needed possibly as a starter that can grow.
Don't know if this helps or not just need a little guidance on the power at this point in time.
Dont know what power supply will be needed - looking for some advice.
The power required depends on each circuit. An Uno with a rf24, a L298 (yuck) and a motor will need a different power than an Uno with a rotary encoder, button and small LED. 10 servos will need a lot of current. A few sensors, probably, little.
So make a list of each Uno (or Mega) and research the current and voltage requirements of each part that will be connected to that Uno (or Mega). Then add the currents for the parts up for each Uno and double the sum.
You seem to miss the point. We need to know exactly what you expect to be powered, in order to give advice.
Hello
Make a energy bilance for all used Arduinos, sensors and actuators.
Have a nice day and enjoy coding in C++.
Not a genuine reason.
Using multiple microcontrollers requires that you use (invent) a complete protocol to communicate between them. Just communicating between two is bad enough, it gets worse.
You sill need to have a genuine reason for employing multiple microcontrollers and making things difficult. 
Try to establish a communication between two Uno's with a single Uno! Then you will quickly notice the advantage of having more than one Uno.
I also own several Uno's, 1 Mega, 4 - 5 Nanos, 2 Pro Minis (5V + 3.3V) and a ProMicro (32U4). As well as some Attinys. So I can, for example, work on several projects or project parts in parallel and, if necessary, also build up the hardware of a forum user who has a problem and help him because I can test the code in a practical way.
Thank you - it will take me some time to do this but will get back to the forum.
This seemed to be my way of thinking when I designed the 'plan', but until now I never thought about the overall power to run them as each subsystem was tested with the mega individually.