I would have thought that you could have purchased some of the canvas strapping "new" from a place that supplies furniture restorers or vintage car trim restorers or a similar place. I wouldn't have thought it necessary to purchase a complete gas mask haversack just to obtain the carrying strap for making watch straps.
Information
Warning: This is a relatively older thread
This discussion is older than 360 days. Some information contained in it may no longer be current.