Kevin,
Is this where you found the information on the 1st Colorado?
"Minimum Required Weapon &c. Buy one. The model 1855 ("type I" or "type II") should be your first choice. A. Rifle-Musket: Model of 1855 Springfield (.58 cal) This was the issue weapon for the First Colorado Volunteers. Buy this weapon if at all possible. The most economical way to get one is to have Tim Oakes retrofit the Euroarms 1861 Springfield reproduction for you. There are two types of the model 1855, but either will work just fine (the basic differences are in the nosecap, front sight, and cap box in the stock). 1. S&S Firearms 2. John G. Zimmerman 3. Lodgewood Manufacturing B. Rifle-Musket: Model of 1861 Springfield (.58 cal) Euroarms: Carried by most sutlers, this product features one-piece walnut stock, correct lock and barrel. All stampings on barrel, lock, barrel bands, and tang of buttplate. Correct "swell" to ramrod, although not as good as the originals. Modern stampings on barrel and trigger guard tang should be filed off. 1. Lodgewood Manufacturing 2. John G. Zimmerman 3. S&S Firearms"
Since the above was from an old pdf file I looked to see if they were still in business and it appears that they are -
http://www.spiralspecs.com/firstco/Unithistory.html
I think I talked to them about joining once at Four Mile Historic Park ( back in the eighties), but life intervened and I never did.
As far as the 1st Colorado in 1862, it appears that they received their weapons at Fort Union in March: "The regiment remained at Fort Union until the 22d of March, undergoing in the meantime almost daily drilling, Here, also, the men were completely supplied and equipped with regulation clothing, arms and ammunition from the government stores." (from The Battle of Glorieta Pass, The Colorado Volunteers in the Civil War, William C. Whitford, page 79).
I also found that the ordnance department at Fort Union had received shipments of the 1855 model Springfields: "The ordnance depot received a shipment of 1,100 "new model rifled muskets' (.58 caliber, designed to be used with the Maynard primers) in 1858. They were known to be defective and the hammers were to be altered by the ordnance detachment at Fort Union before they were issued.", when they started overhauling them, they found even more problems: rust, the screws fastening the rear sights were too long and caused a "bulge on the inside of the barrel", and some of the crates shipped from Harper's Ferry arrived damaged. But apparently all were repaired and ready for issue in early December 1858.
This information is in the National Park Service publication - "Fort Union, Historic Resource Study" here:
https://www.nps.gov/foun/learn/management/upload/FOUNandFrontierArmyOfSW-2.pdf
However, it seems highly unlikely that these rifles would have been around for the Colorado volunteers to use in 1862, as they were intended for the regular infantry stationed in the southwest. There could have been more shipments I suppose but that would have been difficult after the war began since all the states were trying to beg, borrow or steal weapons of any description. I'll try emailing the above site and see if they can tell me where they got the information on the 1855 Springfields.
Dave