Bob, off the top of my head I can only recall two other cases of "mass desertion" of Arkansas regiments, neither of which were associated with the July 1862 plot in the 26th Arkansas.
One incident involved the 14th (Power's) Arkansas Infantry in Mississippi in June 1862. This was actually a mass protest against the War Department's extending their term of service from twelve months to the duration of the war.
The other involved Adams' Arkansas Infantry a couple of weeks before the battle of Prairie Grove. The regiment was comprised primarily of conscripts, who were either pro-Union or at least decidedly neutral. Many of them walked off the job before the battle, and most of the rest skedaddled from the field during the battle--the only documented case in which an Arkansas regiment broke and fled. The regiment was disbanded in dishonor shortly after the battle.
There was an incident in the 36th Arkansas that never actually approached mass desertion. A company captain was court-martialed for encouraging his men to desert, but only a few actually did so. I can't recall precisely when this occurred, I'll have to check my files on that, but it wasn't related to the incident in the 26th Arkansas.