There is this brief entry at Antique Sounds Workshop, apparently from 2011:
“The Adler-Heinrich workshop was forced by economic circumstances to close its doors in late November of 2006. We acquired as many instruments as possible before the shutdown and have gradually sold them off during the past five years. Unfortunately, our inventory is now completely exhausted and there are no more of these instruments to be had.”
Given that ASW seems rather picky about the instruments they sell, I would take this as an endorsement.
I am barely a recorder novice, but I do own a (maple, I think) Adler alto, model unknown, which I seem to have ruined by leaving it unattended through several Maine winters. It had a soft and pleasing sound while it lived.