The NCDC has a huge collection of data that's not on the web, but that is available on a bulletin board, via FTP, on CD ROM, or in printed form. You can also go to the NCDC contacts page where you'll find links that will enable you to e-mail the center with your questions. Our thunderstorm index has more on hail and other aspects of thunderstorms. I'm doing research on hail in Florida. Here you'll find a link to the Storm Chasers Home Page.
Many storm chasers take photos of hail as well as of tornadoes and many sell photos.
It will probably take some clicking around among the many links on this page, but I think you have a good chance of finding what you're looking for. Clicking on the words in color will take you to the National Weather Service's Storm Prediction Center web page where latest reports of severe weather are posted. These are usually very detailed, with information such as the size of the hail from hail storms. It should be what you're looking for.