I think I made a point that the armor Estarossa was wearing in the dream is the same one as Mel's. It was inside Elizabeth's dream who first sees the poster then thinks of Meliodas, and that's when Estarossa shows up wearing Mel's armor and she wonders if it's the real Mel.He was posing as him inside her dream. The druids didn't give Estarossa anything, because it was a dream.Mel on the other hand, the armor could have been given to king Baltra as a gesture, or there is a smith in Liones who comes from the druids(a refugee like Hendrickson) who made the Sins armor. If the STs were given to the Sins by Baltra then there's a chance the armors were also provided by him, or just by the Kingdom of Liones.