I think the blackbirds are discontinued. I don't know why.

Most of my bars seem to be the 25.4 or 26.0 size, I think. I'll have to keep an eye out for 31.8 bars. Ahh, maybe I got one on the Tricross.

I suppose I can see why the 1 1/8" stem adapters are popular, in part because the selection of new stems seems to be lacking.

Here is a 31.8 stem, but like so many, it has an upward angle (MTB?)
Origin8 Pro Fit ATB Stem, 1" Fork Diameter / 25d Angle / 180mm Steerer / 31.8 bar