The pre-'09 E-series did not have a factory switch available, but if you've been in any moving truck, they had them. I'm not sure who made them. For a while, you could buy them through Ryder parts, but I doubt it anymore since the '09+ vans have a factory switch. Might have to find a used U-haul somewhere and try to buy the switch off them.
Other than that, you can disable the airbag (I'm pretty sure all '97+ with the RV prep package had both) by buying a dummy resistor. This will keep the airbag light off, and keep the driver side functioning. You'll have to DIY. In order to get a shop to do it, you have to request a waiver from the NHTSA. Or find one that doesn't know the rule.
https://www.automotivecircuitsolutions.com/products/bypass-simulate-srs-airbag-emulator-simulator-resistor-diagnostic-tool
