The balls look very similar to an 'Omnikin Ball' that we have in our gymnasium -- complete with poly-canvas cover. Typically, the balls are 48" in diameter, but I've found some 40" Omnikin balls on the net.
http://www.athleticimpact.com/ba552.html
http://www.sportsdirectsource.com/products/359
....unfortunately, neither one gives the precise weight.
Patrick