From that image it appears that everything concerning the chassis but the rear suspension would be VW parts.
Still a leaf spring airbag is a common item. Is there something unique that requires it to be a Winnebago specific part?
That model is based on the Volkswagen Transporter EuroVan T-4. Perhaps you can find more info looking for parts info for the EuroVan?
Sorry I’m not much help. But my original suggestion of taking it to a truck suspension shop might be your best bet.
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