Hi Janet,
Here's something that may be helpful: The photo below shows the interior of my Arkel small h'bar bag, with the yellow waterproof lining removed. Those nubby white items you see are 10mm plastic dome nuts which thread onto the four fixing bolts which protrude into the inside of the bag, between the liner and the rear wall of the bag. (These four bolts fasten the attaching brackets to the outside rear of the bag.)
I should think that you could ask Carradice for something like this, or possibly even find something similar at a good hardware shop, or a shop specializing in fasteners.
On my Arkel setup, one of the four dome nuts tends to work loose, so I've used Loctite blue to keep it in place.
Hope that's helpful,
Cheers, John
