So I improvised by sewing a black tab and button on the inside. Not the greatest fix, but at least it's wearable. This is See the World in Black and White boucle from Gorgeous fabrics and there is still a jacket to come. I made a sheath from the same fabric for my SWAP.
Today I bought some buttons for my coat. The left one is the one I wanted, a large concave matte black button. The second one I bought just because it was interesting, even though I am sure I will stick with my original plan. The bound buttonhole will be black faux leather and the inside collar stand is black faux leather. Still not sure about the tabs on the sleeves.
Here's a close up of the second button. It's clear resin with lace set into it. I'm not sure what I'll do with it, but the right project will present itself in the fullness of time.