What exactly do you mean by SOP's, as far as Maintenance is concerned?
Each OEM supplies the Maintenance Manual and each OEM has a different philosophy on how and when certain inspections should be done, as each OEM designs and manufactures their helicopters differently.
Sikorsky use shims everywhere and flight control bearings come "pre-worn".
Agusta/Finmeccanica/Leonardo have heavy well built transmissions but the airframes are built light and seem to crack.
Airbus are easy to take apart and put back together, but you end up doing that on nearly every inspection.
Bell are Ok to work on, but not as easy to work on as Airbus.
MD are just horrible
Tongue in cheek generalisations there, but you get the idea of how different each OEM is.
The standards for how maintenance is carried out in each country is defined by the local Airworthiness Authority (facility/experience on type etc).
So what, exactly, are you after?