If this in the automotive arena, most if not all OEMs have a Supplier Quality Dashboard Application (or similar), that serves as the main conduit for a suppliers part status re: PPAP milestones,production readiness milestones, specification changes etc., my guess is that this is where an updated CSR can be found...or failing that via the OEM Buyer/Purchasing Agent, in either case this change or notice of change must be perfunctory or automatic, allowing for easy access by Tier 1 suppliers...
Hope this helps...
Optomist1