I used to get PB Classic in 5-gallon pails from my local NAPA.
Another CI4+ oil is Mobil Delvac MX, which is only available from Mobil distributors.
These are high SAPS, high ZDDP oils that are not for use in engines that have aftertreatment systems. They were originally formulated for the first generation EGR engines.
Thanks to all for responses.
All the Valvoline Premium Blue Classic at my local distributor are CJ-4, as is every other 15W-40 diesel oil on the shelf.
I've found Swepco 15w-40 which the classic Porsche community uses, but it's at synthetic prices, plus shipping
Yet to try farm supply stores.
OK, just found at (not so) local farm supply store:
Ambra MasterGold HSP SAE 15W-40 CI-4 specified for New Holland equipment. Quart 5.08, gallon 19.38, 2.5 gallon 45.31.
To answer dnewton3's question, based on the following, CI-4 may be ideal for my '20s & 30s designed & built engines.