Silver cup is a bright pink annual Lavateria--a beautiful plant. It is in the mallow family--not a yarrow at all. Most seed companies carry it. You were just looking under the wrong name.

Oh, dear, I messed up! I didn't mean to combine the yarrow seeds and the Lavatera seeds. Yes, the mallow is a Lavatera but the yarrow I have been searching for and forgot to mention is Coronation gold. I grow lots of flowers to dry and the Cornonation Gold is the best yellow or gold yarrow that I've found but have lost the seed source and lost my plants.

True 'Coronation Gold' is propagated from cuttings or division, not seed. That is why you aren't finding a seed source for it.