A friend of mine has a Duo-Art mechanism from a Steinway.  Although
I have not seen it, it sounds to me as though he has all the parts
down to the last bolt.  He is a technician and will be able to answer
your questions.  The price is $900, located in New Jersey.  Contact
Eric Lindeblad,  Shop tel.: 973-361-2172

Good luck

Paul Manganaro