The source I had wasn't so precise about 1946 production levels, but I think 10-12 bombs per month for the first months of 1946 would not be unreasonable. If you husband all the post August production, it could well be over 50 bombs (though I think it very unlikely that that would happen).By April of 46 that leaves you with 45 weapons at least. I’d pursue the invasion with planed tactical use of nuclear weapons, both at the beaches as well as in major operations where Japanese units would be forced into heavy action. Armed forces would be transformed into feelers, prodding and pushing as far as they can without meeting heavy resistance. Once such resistance is noted nuke it until it’s neutralized then move on leaving civilians and such to military police and provisional administration. The Japanese would probably deploy biochemical weapons against US troops so my tactic of dispersal and “feelers” would minimize losses on allied side.
But even allowing for some limited use of bombs for occasional attacks on cities, or for use in MAJESTIC (assuming it actually does happen), it's not impossible that the U.S. could have a few dozen bombs to spring all at once, or in rapid succession, for CORONET come spring. I think The Red did that on a more limited scale in his timeline. Now, you would also have to ramp up conversion of B-29's to Silverplates if you want to do that - not too hard to do, but it would have to be put in train at least a few months before. I think you'd also need to train more pilots for the job, too.
I have to think being hammered by dozens of 20kt range fission bombs on the Kanto Plain within the space of several days would be pretty demoralizing even to the most fanatical army hardliner.