Correct. On solid core blind rivets the core rod breaks off above the rivet head and then you trim the core down flush with some nips and finish-file the sharp edge. They're considered structural rivets for racing purposes and completely acceptable to be used in sheer. I believe must of unions on our frame have them (I haven't taken the time to closely examine the rivets on our frame, so just a guess).
Hollow core rivets (like the ones you get at home depot or hardware store) are typically only used for body panels or other non structural items on a race car...
Availability: McMaster is your friend
Cheers,
TP