Quote from the announcement on 16th december (Steam):
“Players can earn War Coins in a few ways:[…]
Adventure Board - There are 2 Adventure Board Tasks with War Coins (Epic + Legendary) that players may encounter.”
Has this happened already? It’s been two months now. Seems to be the only non-paying way to get these things at this point.
The few from the calendar when this feature was introduced, were not enough to unlock a banner. If they did not want older players to get these items, they would not have included an achievement for it, right?