Try a junk yard or ebay for the control unit, around 80 or so.
Or just make up a jumper wire with terminal connectors remove the relay wires from the front control unit and install the jumper.this will bypass the fan relay and the fan will run via the switch, just don't forget to shut the fan switch off when you turn the van off or it will run and drain your battery.
good luck let us know how you make out