I am looking for Powershell script to copy vhd to subscription using Resource Manager deployment model.
vhd's are stored in Azure storage page blobs, and the storage API works independently of how an account is created (classic vs ARM). It's even independent of subscription. You just need your storage account's name and key.
So you should just be able to copy via something like:
$DestContext = New-AzureStorageContext -StorageAccountName "<name>"
-StorageAccountKey "<key>"
Start-AzureStorageBlobCopy -DestContainer "<containername>" -DestContext $DestContext
And Start-AzureStorageBlobCopy
should work the same, regardless how the storage account was created.