When I got my F motor back from Mile High Performance for me to assemble, they instructed me to add a quart of ZDDP for the break-in oil. I went to O-Reily and asked for it, and they looked at me like I had an eye in the middle of my forehead. I explained why I was asking and we went and looked at their shelf of additives. Sure enough, there was a quart of something or other that when you read the label closely it said it was ZDDP, but the ZDDP parts wasn't featured prominently in the name or in large print on the front. I thought I took a picture of it to remember what it was, but can't find that picture right now. It came in a yellow plastic one quart bottle, I believe it was around ten bucks I think?
Back in the day I used to use CLM, which had zinc, copper and lead microspheres suspended in an oil base, you added a bottle to your oil when you filled it at change. Those bottles were maybe 6 oz. or so? I think they were based in Colorado and I remember trying it after Tom Martino tested it and got good results. I haven't seen it in years, I wouldn't be surprised if the formula was regulated out of business due to the lead.