Over the past 40-plus years I have seen dozens and dozens of the Bianchi shoulder holsters with elastic straps that have worn out. Never was able to locate a source for really heavy duty elastic strapping, so I started making up straps using soft woven nylon strapping with sliding fasteners for length adjustment. These are not affected by perspiration and body heat as elastic is, so they retain their strength for years. Before retiring I usually kept two or three of these on hand for those in need, and I think I have one left. Send me a PM with your mailing address and I'll send it to you, then I'll have one less thing hanging around to deal with!
Best regards.