First welcome to the Stovebolt.
Charlie, I know you want to do it right but for me I gave up on the cussed rivets I was sent. Even using the tool I bought with them it turned out to be a big pain. So, I used some good 3M adhesive, glued them on and have never looked back.
But, to answer your question I feel sure that JimCarter, American Classic or one of the other vendors listed in the links here on the bolt will have them...... but I have also noticed some of them have quit carrying some of the little stuff they use to. Someone who has recently ordered them may chime in soon.
Good luck on the project.
EDIT: Vent assembly rivets. Here you go.
http://www.classicparts.com/Retainers-Hardware/products/812/2/0
