Europtic has had the Lapua 50 BMG brass listed since mid-May - for PRE-order with expected delivery in June. Their pricing is $254/50. See Lapua 50 BMG Unprimed Rifle Brass LU4PH1200 for sale!
You need to call them and get on the list. They require a deposit of 20%. [I have one box on order to compare with the RWS I have.]
Graf also has it listed but for quite a bit more, $283.99/50 - see Graf & Sons - LAPUA BRASS 50 BMG UNPRIMED 50/box
Europtic has picked up a lot of Lapua ammo, brass, and projectiles. Their price for 338 LM brass is very good (best I have seen), $256/100 - see Lapua 338 Lapua Unprimed Rifle Brass LU4PH8068 for sale!