Don't know why I missed your last post.
A metal stretcher or shrinker uses flat plates with teeth on them to kind of "stretch" the metal, thus making the circumference longer, and creating a flanged circle. I think you could check the online catalog for Aircraft Spruce & Specialty.
I was at an auction this past Saturday at an Amish farm. One of the items was a LARGE metal stretcher. The owner said he used it to work on steel up to 1/4" thick, and the horizontal part of the flange about 2. to 3" wide. Would make some pretty large flanged pieces fairly quickly, no forge needed.
Mine is much smaller, and I mostly used it to make aluminum flanges from .062 stock. The jaws on mine are also dual purpose, being able to shrink as well as stretch. The guy's large one weighed about 150 lb., mine weighs about 1/100 of that!
Either way, bet you got that bellows all sorted, and blowing good air. Envious, but to old to be forging stuff!