You could buy the white blanks from PMK and then dye them with iDye Poly.
PMK have black 2.25u SA, no black in 2.75u SA though.
I feel your pain - the genius that I am I designed my board with 3u caps and now I'm painted into a corner. I managed to get a couple black 3u SA off PMK before they sold out but they're not pleasant on my thumbs - I recommend narrowing your search further to convex which probably doubles your trouble.