1. The Donetsk self-defense forces have announced on 29.06 that they have captured some Buk systems from Ukranian military. Presumably with some ordnance.
2. As of yet it is not proven that Donetsk forces have shot down that plane or even that anyone shot it down (could have been an onboard explosion).
3. Even if Russia has sold them or given them some missiles target selection was not done by Russian citizens or military.