Make sure they still issue a warranty with the genuine oil - if not i would actually accept the Castrol oil for this time. But there should be no reason for them to decline warranty when you supply the genuine oil!
I am fairly sure you can get the LM0 oil more easily in germany, part number is 77 11 172 226 (2 litres)
It is in my oppinion bullshit that they have to order more than your requested amount in denmark, as long as you accept 2 litre bottles (2-4-6 and so on). They are sold as pieces from Renault like any other spare parts, problem is that Renault Nordic dont stock this oil anymore for whatever reason, and Denmark also are bound to Renault Nordic ? So they have a week delivery time from France
I cross my fingers that you will make it there with your box! Just take it easy...