Is a hi volume oil pumo needed when building a turbo efi a14 running atm 10psi or eill a standard ine be ok.

I would say at a minimum a new std pump, maybe bump the pressure a little (but not too much!).
If you can find/afford a high volume then go for it as it's just added insurance..

I want to run a high volume one but can't find one any one know of where to buy one.

As far as I know, an off the shelf high volume pump doesn't exist for the A-series [exception being the nismo competition item].
It is do-able however to make a hybrid pump using the internals from a L-series pump and 2 X A-Series pumps [1 off the A-series pumps is sacrificed to be used a spacer as the L-series internals are longer.

handy link hybrid A-Series oil pump

We do you recommend higher pressure?

Datsun Competition had a high-volume pump for use with a remote oil cooler.

I heard you southies (people from new south wales, not being racist) like to just bump up the pressure of the standard pump and run an oil cooler to increase the volume of oil instead of nice mods like a baffled sump and increased volume oil pumps.

Baffled sump is to help keep the oil in the bottom of the sump even with high G-forces of racing.

What is the increased pump volume for?

Increased pump volume will cut the time it take for oil pressure to come up at start up, especially when using oil coolers that drain back to the sump when the engine is switched off.

Also when fitting other things to an engine that efectively create a leak in the pressure side of the oil system. Eg. A turbo (especially the foating bearing type). These will bring the standard pump closer to the point of not being able to maintain good oil presure.

A small volume reserve is good insurance angainsed increased bearing clearances as the engine wears and if a leek occurs (maybe an oil cooler line) oil pressure to the engine bearings is more likely to be maintained (hopefully you realise there is a problem before the sump empties!)

I must add that i have not tested the reserve capacity of the standard A series pump and it might have enough capacity to maintain good oil pressure with a turbo and hot oil.

I have a datsun competition two stage pump on my turbo engine and it only just has enough presure when the oil is hot and at idle (10 PSI) and that is with a ball bearing turbo that needs a lot less oil than a floating bearing type.

Also, performance motors are generally built with clearances purposely on the large side, thus more leakage of oil when operating and the risk of dropping pressure.
Unused capacity from a high volume pump is just returned to the sump via the pressure relief valve. BUT there is extra capacity should you ever need it!

I am guessing the downside is the extra power required to drive it due to higher pumping losses and thus the load on the cam/engine?

Aren't the nismo A seres pumps like the ones the 308 holden used? Bloody hard to prime.