I've been in touch with Bill Lomas of E.J. Thomas Mercantile about reproduction 1862 Sharps Rifle cartridge boxes. He is within reach of two originals to study in person and might be able to produce them with quality tins and wooden blocks. If anyone here has seen Bill's work you know that it's top quality. Some of his products can be seen at The Regimental Quartermaster in Gettysburg, in a display case at the check-out desk.
Aside from Jarnagin, there is someone else producing what looks like a good Sharps box but I have not handled a reproduction of it in person. Mike Brase had one for sale on eBay a week or two ago and it looked like a well-made, solid reproduction. I intended on buying one as a sample but completely forgot about it and now it's no longer for sale. Photos of Mike's Sharps box can be seen at this link:
https://www.facebook.com/media/set/?set=a.177031362424236.35610.177013229092716&type=3The standard issue .58 cal. cartridge boxes with strap were indeed issued throughout the war, and with plates from time to time. They first appeared with the Colt Revolving Rifles and some may have been retained when the Sharps rifles were issued in the spring of 1862 depending upon their functional condition. For instance, two sharpshooters pictured below are showing off their newly issued Sharps rifles while in Falmouth, VA, and both are wearing what appear to be .58 cal. cartridge boxed with straps.

Frank Carr, Co. G 2nd USSS. His cart. box strap has a breastplate that appears above his left wrist; note that he is wearing his accoutrements incorrectly so they would appear to be in the correct position in the finished image (wet-plate photos are reversed).

Thomas Reese, Co. A 2nd USSS
A small handful of sharpshooters photographed around the same time as Carr and Reese have both the Sharps rifle and Sharps cartridge box. Not only were the Sharps boxes issued with the rifles, new bayonets and bayonet scabbards arrived as well. Bill mentions the issuance of cartridge boxes with straps and plates, which was done, but I recall an account from the 1st USSS of Maj. Charles Mattocks (17th Maine Inf., sent to shape up the 1st USSS in early 1864) trying to do away with the .58 boxes and replacing them with Sharps rifle cartridge boxes. I don't have the citation here with me but maybe someone else does. At any rate, Mattocks was a stern military bureaucrat so it's no wonder that he would try to have the men use cartridge boxes that were made to be used with their Sharps rifles.
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Brian WhiteWambaugh, White, & Companyhttp://www.wwandcompany.com----------------------------------
Randolph Mess, U.S. Sharpshooters