It's produced by a Raijuu which can be captured at the El Arma Gravesite and kept at the Big Farm - best capture two at least, you will need two as part of a later quest. For the bucket Use mythral ore to make mythral bar then use the yellow essence to enhance the bar then use two to make a bucket.
Yeah, the whole armours thing is a bit of a slog, but no way around it other monter girls you will need two of are - Anubis, Thunder Kitty and Ice Harpy - Probably never even see the armours.
