Thank you for all the replies!

I ended up getting some gore-tex mitts at a used-gear store.

I figure I can wear my thin-ish wool gloves underneath as liners. They just breathe so well. I hope they still breathe through the gore-tex outer layer.

Sad, though, that the wool-glove manufacturers don't appear to offer any truly waterproof gloves or mittens. I would sure love that.