OK, I found 2 places (CC Parts and Powertoolreplacementparts) that claim to have the 84005207 camshaft.  The latter has the better price.  They don't have any fitment information and seem to only do that via e-mail... no telling how long that dance would take.  So I am going to trust the cross reference AVB posted above and order the thing.  Hopefully won't take too awful long to get here.  I'll hang onto the 793880 until I am sure this new one will work, then send it back to Amazon.

The new 84005207 cam came and seems to be identical to the one that failed in this 2014 mower.  Both are stamped "579".  The only difference I can see is that the compression release lever is stamped "G" on the old one and "J" on the new one. The broken pieces I fished out look identical to the intact new ones near as I can tell.  In any case it is here.  But it did NOT come with new tappets like the older cam, so I will reuse the original tappets that seem to be in really good shape.
 
One thing I am not sure about is this other pin I fished out of the crankcase with my stick magnet.  See the red circled piece below.  Anyone know what that is?  Maybe it is the base of the compression release pin that was pressed into the release lever from which the d-shaped pin broke away from?  That's my guess anyway.
 
Edit: Looking closer I am sure that the round pin is (or was) part of the compression release pin that went into the main gear.  You can clearly see where the d-shaped part of the pin snapped off.  I feel better now.  I know that I got all the broken bits out of the crankcase and don't have anything extra in there that is unidentified.
 
 

raylo
The new 84005207 cam came and seems to be identical to the one that failed in this 2014 mower.  Both are stamped "579".  The only difference I can see is that the compression release lever is stamped "G" on the old one and "J" on the new one. The broken pieces I fished out look identical to the intact new ones near as I can tell.  In any case it is here.  But it did NOT come with new tappets like the older cam, so I will reuse the original tappets that seem to be in really good shape.

Thanks for the heads up about the tappets not being include with the new part. Another sneaky Briggs parts supersede. I got make a note of that here as I always change the tappets.

And here's another thought.  This new cam looks exactly like my old cam, so maybe the "new" part number cam isn't really a different design and was implemented merely to remove the tappets so they would have to be purchased separately.
 

AVB
Thanks for the heads up about the tappets not being include with the new part. Another sneaky Briggs parts supersede. I got make a note of that here as I always change the tappets.