Unfortunately, the '64 Zolatone color is no longer available. For touch-ups that small on our '64 I went to a model train store and got several different colors and just touched up the rivets with a tiny artist brush, dabbing the different colors to simulate the Zolatone texture. With patience, they look pretty good, your'e not going to find the same color Zolatone - it's a discontinued color, and a typical spray paint is just going to look flat. The idea is that they just disappear, which is better than leaving the silver rivets unpainted...they blend in and you just don't see them.
On our '56 that we re-Zolatoned during our restoration, we have leftover paint. For tiny areas, like a rivet - same thing, just dabbing the Zolatone with a artist's brush will blend it in. For larger touch-ups or more than half a dozen rivets at a time, you can buy a small aerosol-type can and put the Zolatone in it to spray it. We use a piece of cardboard with a hole in it to protect the surrounding areas. A picture of the Spra-Tool is attached below. But sorry, this isn't really going to help you with your '64...
Shari