This is the type of rivets used on a B-Body Heater Box. The second link is to the tool. Match up the size you need. I'm sure there's other sources to.

http://www.mcmaster.com/#tubular-rivets/=f7veuk

http://www.mcmaster.com/#6667a/=f7vgg1

Scott

70 Coronet RT 440+6
64 Dodge 330 - Future Hemi Clone
17 Challenger Hellcat - Green Go Driver
86 Buick T-Type Turbo V-6