This will be a weird one maybe, but...

California friends:

I, until recently, had a 2017 4Runner S45 Premium. My wife was in increasing need of parking sensors, as she began driving the truck more. As these were not available at the time when purchased new, I secured material to do it as a DIY. I have a sensor kit ordered third party from carid.com (might have been iBeam, or BrandMotion, can't remember) which is basically the sensors for the rear, wiring, and then the display module you tuck into the cockpit somewhere. I also secured a 4Runner Limited rear bumper cover from another person, specifically for this purpose (with the knockouts for the sensors in it so that you don't have to drill your stock bumper cover.)

We never got around to it, things got real, and we sold the truck and got a new '21 Limited Nightshade, with aforementioned sensors.

SO: I have the sensors, and the bumper cover, available to you, for FREEEEEEE. You just need to be local enough to come collect them. I am in 94960 in Marin, so anyone farther north, in San Francisco, in East Bay, in San Jose, easy enough to get to me, and I'm happy to hand this project off to you. Let me know!