Finding a script that fits exactly what you want is more luck than probable. Get-ADUser has a parameter to limit the scope to an OU, you just need to update the command to return what you want:
-SearchBase
Specifies an Active Directory path to search under.
When you run a cmdlet from an Active Directory provider drive, the default value of this parameter is the current path of the drive.
When you run a cmdlet outside of an Active Directory provider drive against an AD DS target, the default value of this parameter is the default naming context of the target domain.
When you run a cmdlet outside of an Active Directory provider drive against an AD LDS target, the default value is the default naming context of the target LDS instance if one has been specified by setting the msDS-defaultNamingContext property of the Active Directory directory service agent (DSA) object (nTDSDSA) for the AD LDS instance. If no default naming context has been specified for the target AD LDS instance, then this parameter has no default value.
When the value of the SearchBase parameter is set to an empty string and you are connected to a GC port, all partitions will be searched. If the value of the SearchBase parameter is set to an empty string and you are not connected to a GC port, an error will be thrown.