Currently it would be a custom order.
There were many thousands of the Shapleigh King Nitro 16 Gauge with a double barrel. For the most part, they are worth about $50 to $100 depending on mechanical and finish condition.
i got a 12 gauge king nitro double barrel double triggers and double hammers no serial number on it
50-100 USD
The 12 gauge King Nitro number 3411 is likely a vintage shotgun manufactured by King Nitro. It may have a 2 3/4" chamber and be of good quality, but specific details about its features and history would require further research or inspection by a gun expert.
BLue Book of Gun Values
50-100 or so
King Nitro was a trade name used by Shapleigh Hardware of St Louise on guns made by Crescent Firearms and J. Stevens Arms.
Single barrel, tops out at $75. Double-barrel, tops out at $175. sales@countrygunsmith.net
Seldom exceed 125 USD
NITRO KING was a trade name used by Sears on guns they retailed through their catalogs in the late 1880's through World War I. There is no appreciable collector value, and these guns are generally considered unsafe to fire due to the twist steel barrel. Value would be in the $50 range. sales@countrygunsmith.net
Nitro King was a Sears Roebuck brand name made by Crescent Arms, 1908-1917.
You have already identified it as a Shapleigh's King Nitro. Shapleigh Hardware was in St Louis Missouri from the mid 19th century until the middle of the 20th. Their King Nitro guns were manufactured by W.H. Davenport and later by Stevens/Savage.