The Steamer "Fairplay" was captured on the Louisiana side of the Mississippi river above Vicksburg by Federal Gunboats with about 5,000 of these arms and other equipment. There was quite an extensive debate between Holmes and the Confederate Secertary of War Randolph along with an inquiry investigation about this incident.
A simply word search of the online versions of the O.R.'s of the word "Fairplay" or "Steamer Fairplay" will get you to the right place.
The particular incident that involved the weapons from the Memphis area occurred in August of 1862 when General M.M. Parson's Missouri Infantry Brigade was transferring back to Arkansas from Mississippi. They crossed the Mississippi River at night on flatboats north of Gaines Landing and brought with them a large wagon train, of I believe some 100 wagons, loaded with supplies for the Trans-mississippi. That train included 25 pieces of artillery other than those which was assigned to that Brigade. This resulted in some five or six batterys of artillery to be organized and armed such as Hart's Dallas Artillery Battery and Zimmerman's Battery. Many of these weapons (Artillery) were lost at Arkansas Post. A clue to this incident is given in "Brothers in Gray" about Parson's Brigade, and in Hindman's Copybook of Telegraphs. But since it was a highly dangerous and secret move it was kept quite in most official communications and little was written about it as I have found.
As a postscript the Troops of Walkers Texas Division in April of 1863 complained about the poor state of condition their weapons and how old they were. They actually looked forward to fighting the federals in Louisiana as an oppertunity to rearm themselves with Battlefield reissues.
Hope this helps