Hi I'm new here and have searched this issue and honestly I go in circles as the 1985 22RE seems to be famous for valve noise. I'll tell my story and see where it goes. Thanks in advance for your help.

Story:
The truck is actually the base for a 1985 Toyota Escaper mini camper with ~75,000 miles and a 5 speed manual transmission. Yes, I know there are specific forums for these campers but the truck engine is the same and figured more experts hang here. August of last year we were headed on a trip and 3 miles in (just warming her up) and the valve train's typical noise suddenly got VERY loud and aggressive so much that it was loud enough in the cab to be concerning. I stopped right away and at idle popped the hood. Sure seemed engine related so I turned it off and I thought maybe I spun a bearing. Noise follows engine rpms. I let it sit a few minutes and it was still there when I started it. Since I was only 3 miles from home I decided to nurse it home and a few 100 yards down the road it stopped. After it was ok for a mile or so I got a bit more aggressive driving it and all was well. Just the normal noisy valve train. That was our last trip for the year so I put it in storage and did research over winter. This spring I adjusted the valve train warm 8 & 12, changed oil (10-30) & filter (cheap Fram), changed cap & rotor as they were a bit pitted, new oxygen sensor, verified right side timing chain guide was still there and NOT broken = all good and looks to be original plastic version. Also checked and adjusted the timing. It was a bit advanced and I did use the jumper like you are supposed to. Took it for a test drive 10 miles or so and I ran it pretty hard = all good. Took it for 2 more test drives of 10-15 miles = all good. Went to take it camping last weekend and 3 miles in the LOUD ping/knock returns. Shut it off and sit 5 mis back on and still there. Head home nursing it and 200 yards later all better. I checked last night to verify all plug cables firmly on and no vacuum leaks. I've only run it around the driveway since getting home but still bad noise has not returned. I'm going to take off the ERG this weekend and clean it out, add some zinc additive to the oil, I'll replace the Fram with OEM oil filter also. PS - No check engine light when this happened recently. I can't recall if it came on last year,

Questions:
1) I want to replace the knock sensor but they have been discontinued with no replacement part number and I can't find one anywhere. Checked the knock sensor wire and it looks ok as some posts say they get crusty from heat. I saw a post from several years ago where others were giving the person some crap and sending links for them that they were "easy to find" but those links were either dead or pointed to out of stock/discontinued. I, as that person did then, am having no luck finding one. This is what I believe I'm Looking for: 1984-1989 Toyota 8961535020: Toyota 89615-35020 Knock Control Sensor. Who knows where to get one?
2) Any other recommendations on what this aggressive ping/knock could be or how to diagnose/fix it?

Thanks Again - Joel