COLT NAVY 1851 SERIAL NUMBERS
YEAR & SERIAL NUMBER YEAR & SERIAL NUMBER YEAR & SERIAL NUMBER
1850 ---------------- 1 1858 ---------- 85000 1866 ---------- 185000
1851 ----------- 2500 1859 ---------- 90000 1867 ---------- 200000
1852 ---------- 10000 1860 ---------- 93000 1868 ---------- 204000
http://www.vincelewis.net/coltnavy.html
So it would have been made in Hartford in late 1858 or early 1859. As to the rarity, you would need to hear from someone more expert than I. Stan