Maybe they could be spun?

If you're not already familiar with it, "Spinning", or "Spin Forming" is forming a disk of metal over a mandrel on a lathe. It's difficult to describe, but once you see it, it makes sense.

The actual spinning starts in this Youtube video at about 2:33.

Do a search on "metal spinning". Maybe a spin former would be willing to do smaller quantities.
Okey-dokey. What's plan B?