I haven't seen ADG or Peterson in stock anywhere, and I am unfamiliar with Lapua even making that case.
I did score 200 new Norma cases not too long ago for just under a buck a pop. Up until that point I had been using 1xF Federal brass with good results.
8m curious to see how the 7mm RM and a few others fare once the 7 PRC becomes plentiful.
It appears it could be a mistake by the powder company listed below saying they had 7mm Rem Mag cases from Lapua or could have possibly been a small run actually made by Norma with the Lapua name on it. Either way I think you are right that Lapua probably never made 7mm Rem Mag brass.