re percussion guns: caps were being used in fair amounts well before 1836 - here are some period citations for the late 1820’s-the 1830’s
1) In 1827 the "American Shooter's Manual" noted that eastern sportsman were almost exclusively using shotguns fitted with percussion locks.
2) General Ashley 1829, "I have used the percussion locks locks but little, but believe them admirably well constructed for general use, but more particularly for the prairies, where the severe winds and rains prevail at certain season of the year."
3) In Sept 1831 and again in December 1833, the US government ordered for the Western Indian trade, some 2150 guns from Deringer. One shipment included," 217 percussion and 93 flintlock rifles complete, at $12.50 each: 217,000 percussion caps at 80 cents per thousand; [and] 310 woolen covers at 37 1/2 cts......"
4) In 1834 shortly after founding Fort Hall in Idaho - N. Wyeth and his party - "percussioned three rifles, our powder being so badly damaged as to render flintlocks useless."
Here's Nat Wyeth's journals/correspondence -
http://roxen.xmission.com/~drudy/mtman/html/nwythint.html5) August 1837, Osborne Russell's hunting companion, "shot a Grizzly Bear and bursted the percussion tube of his rifle which obliged us to return to our comrades...and make another tube." Journal of a Trapper
http://roxen.xmission.com/~drudy/mtman/html/ruslintr.html6) Famed Mountain Man, Jed Smith was killed by the Comanches along the Santa Fe Trail in 1831 - the pistols reputedly taken from him which were reportedly built by Creamer, had been converted from flint to percussion.
7) H. H. Sibley after a hunting mishap, 1839, "........Now my opinion...is that, any man calling himself a sportsman who will not use a percussion, when he can procure one, in lieu of a flint-lock gun, should be furnished with a strait jacket at the public expense."
The US Armies Hall breechloaders were first fitted with percussion locks in 1831 (surprisingly early considering that the miltary of the time was notoriously slow about modernizing).
9) It didn't take long for the percussion system to move west, early in 1832, John Martin of Little Rock, Ark. advertised, " Guns and Pistols with common locks, fitted with percussion locks, at the shortest notice." - In other words he was advertising that he could convert ones "common lock", i.e. flintlock, to percussion at short notice, indicating that there was a plentiful supply of not only parts, but caps as well.
10) American Fur Company brigade leader Lucien Fontenelle bought his Hawken in 1832 and it was definitely a percussion since he also bought caps at the same time.
11) Mtn Man Kit Carson was an early (circa 1839) advocate of Colt's percussion revolvers and longarms, as were the Texas Rangers (1837-38) and Josiah Gregg (1839) and his brother who were outfitted with Colt revolving pistols and rifles.
12) Warren Ferris 1830-35 mentions using a cap lock during his tenure in the mountains.
" Don't forget," cried my comrade, "that all my hopes of salvation are centred in your rifle-ball." The animal was feeding quietly, and I was enabled to approach within some sixty yards of him, when levelling, I pulled trigger, — but the cap, being damp, burst without a discharge . The noise caught the quick ear of the buffalo, and caused him to look round;— however, seeing nothing to excite his alarm, he soon resumed an employment more agreeable to his taste than needless vigilance.
Having put fresh powder into the tube, and supplied it with another cap I was again raising to take aim, and had brought my piece nearly half shoulderward, when it unceremoniously discharged itself, burying its ball in the lights of the buffalo —the very spot I should have selected had it been optional with myself." (NOTE: since the cap went off with a loud noise I doubt it was the cap. but rather a plugged nipple or drum)
Availability of caps in the west:
Hansen's book "The Hawken Rifle It's Place in History" has several references to caps being available in St Louis at least by 1830, just 3 short years from the time they were considered de riguer in the "East" (as noted above in the 1827 the "American Shooter's Manual"ll).
By 1834-35 several vendors in the St. Louis area were advertising quantities of caps in the 100,000's and within another couple of years later they had them in the millions.
As to getting them out west, although it may seem on the face of things that such "luxuries" were hard to get many rendezvous trade lists don't necessarily uphold this view and at least one lists 500 caps.
Not only that, but by the late 1820's and early 30's there were several forts and trading posts in the west besides the rendezvous sytem (which completely died out by 1842). To name but a few:
Uncompaghre in western Colorado(1826)
Ft. Laramie in south central Wyoming(1834)
Ft. Union (1829) and it's satellites in various parts of Montana
Ft. Hall in southern Idaho (1834)
Bent's Fort and it’s satlellites in eastern Colorado (1834)
as well as the Santa Fe trade made things more easily available.