If you can get the KW part number (yes they are KW parts) NAPA can get them for you far cheaper than a truck dealer. They can also get the shocks too,as they are probably due for a change.
I did the same job on mine I took one off and took it to all the dealers with no luck. This is a unique bag the only place besides alumibunk was Fleetpride they had all three in stock for $50 a piece.
Also due to the great design of their products you can not get the bags out unless you jack up the sleeper to at least normal ride height and wedge wood between the frame and sleeper then you can get them out.