When I bought my 1858 Remington, it came with a spare cylinder....while it seems like it might be convinient, I dont remember seeing this 'technique' used much or spoken off in historical documents, documentaries, ect.
How common of a practice was it for military leaders to carry spare loaded cylinders for thier revolvers?
It wasn't, so you are correct in your recollections. Although the Patersons without loading levers came with a spare (and Josiah Gregg speaks of carrying a pair of Colts pistols and a Colts rifle, all with spare cylinders in 1839), it wasn't at all common and in the US service, they were never issue. (There is the possibility that the 50 Colts rifles that Col. Harney purchased from his own funds from Colt for service in Florida had them, but they weren't exactly "issue")
Both the Prussian and Austrian Navies DID issue spare cylinders for the Navy Colts that they purchased, however. The holsters that were issued with them that have the spare cylinder pouch attached (rather like a magazine pocket on a Luger holster) sometimes come up for sale in auctions, but that's about it as far as any government ever issuing spare cylinders, anywhere that I am aware of. I would love to hear otherwise though.
For the War between the States, it was discovered fairly early on that it's a heck of a lot more convienient to just carry a spare revolver than a spare cylinder (though spare pistols were never issue either). And I know of no records at all suggesting that either Remington or Colt ever manufactured "extra" cylinders for sale on any large scale either prior to or during the war (other than in the Paterson period for Colt, and the above mentioned contracts to Europe).
So really, it's all a total reenactorism. Guys are used to the idea of having a spare magazine for their autoloader, or speedloader for their double-action revolver and want that in a caplock too. But the people of that era were coming from a mindset of "Wow, SIX WHOLE LOADS!", being used to single-shots, rather than our "Gee, only six?" today. So a couple of packets of combustable cartridges in the pocket were about it as far as reloads go for most of the guys in the period.
I hope this helps!
Cheers,
Gordon