They used to be available at Team Wagoneer's website
GRAH! O_o
Most of the aftermarket manifolds needed plugs because they're universal and I believe AMC used them to cap factory fresh ones until they ran out of the old casting.
It finally dawned on me less than a few hours since I posted this that 18m is a VERY COMMON thread but any bolt bigger than 3/4" is the major outlier that makes finding these next to impossible. Add to that my issue of figuring out how to search for specific bolts(for future reference the tag is
7/8"-18m) and this issue is just a huge mess. My mind is focused on the wrong stuff. I'm in the wrong headspace. My friend's Hornet uses this size and I have no idea why. I'm guessing his rebuilt 232 isn't from a Hornet but some Wagoneer that has these HUGE oil pan plugs that have been immediately put out of circulation ever since the last J-anything. The support still exists but it's barely there and way overpriced. Dorman part# is 090-011 and it's a real chore to find whether you're at O'Reilly's, NAPA, Central, Fastenal, Airgas, hydraulic shops or tractor supply places.
I was lucky enough to get mine from a NAPA in the next town for a few bucks. Most shops like Baxter want $$. Now I can finally reuse my intake manifold. Yay.