Which bracket are you interested in- the ashtray mount or the console mount.
One of them at least is available as a reproduction- but I don't see it on ebay now.

I have the ashtray mount on mine, but I can't provide pix. I'm building a house right now so my unending Firebird project is in storage right now.
I can, however, describe them, if that helps.....

The ashtray mount is a hanging mount, similar to the CBs and accessories of the 70s. its about 1.5" wide and spans across the top of the unit, and attaches to both sides, with one or two screws. It mounts just below the ashtray, centered up with the burlwood of the center panel.

The console mount is actually two brackets, one on either side. They are typical "L" brackets, about 2" wide, using 2 screws each, about 1" apart. This is why, on some Firebird consoles, you will see four holes in the back of the console.

All the hardware is stamped steel, painted flat black.

When mounted, the distance between the unit on the console and the upper dash is so tight, it's hard to tell which mount is being used. Obviously, if there is no console you have to use the ashtray mount. I'm pretty sure I found a Pontiac document somewhere on this site that said manual trans consoles had the bracket on top, while ATs had it mounted on the console. When I bought my car in '81, the 8-track was long gone, but I am certain that the original console did NOT have those four holes.