If that ferrule has ivory looking grain,I don't think the exact material is available anywhere other than people with a NOS stash.
What I do is explain to the customer that the material is unavailable,but it will work out better if I change it to something else because newer materials are simply tougher.
I've done over 100 replacements on old Meucci shafts where that material cracked from breaking,it was a ABS type plastic but especially brittle when combined with the full 3/8 tenon,they were still coming out at 13.25mm stock back then.
The creamy ABS Atlas sells is close. Juma,the ivory grained Elforyn,and Tomahawk are all better materials,but still liable to crack with 1/16 sidewalls. Tommy D.