Best I can suggest is Bill/GPA selling you complete kits less the cabs [factory plans available], though of course the shipping cost, or......seen a lot good components, speakers being sold around the world on these FB groups:
Altec horn loaded speakers: Altec horn loaded speakers Public Group | Facebook
Vintage Altec Lansing Loudspeakers GPA: Vintage Altec Lansing Loudspeakers GPA Public Group | Facebook
The horn speaker marketplace: The horn speaker marketplace. Public Group | Facebook
James B Lansing Audio Society (Altec Lansing & JBL): James B Lansing Audio Society (Altec Lansing & JBL) Public Group | Facebook
Loudspeaker parts: Mids, Woofers, Tweeters, Crossovers and more: https://www.facebook.com/groups/637510137014242/
GPA speakers looks great, but it isn't equal to genuine Altec Lansing speakers. That means, I need to recalculate boxes, etc. Now I am living in flat and do not have conditions to built my own speakers cabinets.