Personally, I would purchase a suitable size zip off the Bay and replace it myself - given time and patience, it cannot be that difficult, the bag is PVC material not leather, using some suitable cotton thread I would hand stitch picking up the original stitch holes in the PVC. There are all sizes/types and colours of zip on the Bay!
The bag on my Centenary had the dreaded crumbling plastic handles - it's a common one and apparently, they even can deteriorate in the box. Took me some time but I found some suitable genuine leather handles on the bay, even colour matched to the tan/brown of the bag - okay, so not 'original' but actually, they look and perform better than the originals, so okay for me!

ASM