Jaime Hernandez:
In 1968 the United States Mint began producing 1968-S Proof Kennedy Half Dollars at the San Francisco Mint. The coins also displayed the "S" mint mark. The last time the Mint produced Proof Kennedy Half Dollars was in 1964, but those were produced at the Philadelphia Mint. The 1968-S Proof Kennedy Half Dollars came in much better quality than the 1964 Proof Kennedy Halves, proving that the workmanship was much better at the San Francisco Mint.
Collectors should not have a difficult time finding nice examples of this issue, as most examples can be found in high grades. Examples up to PR68 Deep Cameo condition are fairly easy to find. However, in PR69 Deep Cameo and higher, they are much more difficult to locate.