Air bag Replacement - Front and rear

I have a 2002 Winnebago Journey32T.   The techs working on the vehicle recommend changing  out the current airbags (they bear the Firestone logo).  The parts people where the vehicle is being serviced have been able to locate replacement bags for the front axle.  They have not been able to locate replacements for the rear, drive axle.  Firestone has said they do not have a replacement for the rear bags that are on this vehicle.  Does anyone have a recommendation for a brand and a supplier of that brand in the Spokane area of Washington or in the Bitterroot Valley of Montana that, or an internet provider from which replacement air bags for this vehicle could be obtained?

I appreciate any suggestions..