US half dollar coin was first introduced in 1792. But it was not minted until 1974. It has several versions since it was first issued:

• Flowing hair (1794-1795)
• Small Eagle Reverse (1796-1797)
• Heraldic Eagle Reverse (1801-1807)
• Capped Bust (1807-1836)
• Liberty Seated (1839-1891)
• Barber or Liberty Head (1892-1915)
• Liberty Walking (1916-1947)
• Franklin (1948-1963)
• Kennedy (1964 to current)

Here are some liberty seated half dollars for sale on eBay.