The button is held on by barbs on the small rod that it fits onto. I had a similar problem on the '74, but I found that I could press the button back down on the rod far enough to get it to stick...that was many years ago, and it's still holding. Ya'll might give that a shot, but you'll have to be careful, cause the button might split, or you could bend the rod, if ya get to forceful. I used a small, rubber mallet to gently persuade mine to go back on. You can also use super glue, or maybe some kind of epoxy to help hold it on, but I would try it dry first, just in case the button just needs to be installed a little deeper on the rod to hold it.
Realize, too, that the later cars have a different p-brake handle set-up, so this may or may not work on yours....I'm just saying it worked great on mine.
I don't think anyone is reproducing just the buttons, but there is at least one guy the is doing restos on the p-brake handles, including re-chroming the plastic, and new buttons...
______________
Joel Adams
C3VR Lifetime Member #56
My Link
(click for Texas-sized view!) NCRS
"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"