For those of you still wanting to do this I've found this on Amazon:
Amazon.com: 2pcs High Quality Heated Pad Kit 2 Seat(4 Pads)Heater for TOYOTA PRADO: Automotive
$74 and it looks like it just wires in as a "universal" setup using the 4Runner switches. Not sure if that is true or not but that's a good deal even if you just want the switches! I am NOT affiliated with the seller but I will be buying that soon for my MR2.
I actually emailed them asking about compatibility and this was their response:
"Good day! Thanks for your message.
As to this issue, the item can be directly wired into the vehicle.In addition, the item is not Prado specificas long as the vehicle can drill the hole.Hope it can help you.Thank you!"
WVS,
Thanks again for your great write-up. I completed the job on my 4th gen and now ready for the cold! There were a couple of minor differences between the 4th and 4th gen systems but I manage just fine. I'll post in the 4th gen forum as well in case anybody is interested.
Cove