Manufacture of Old Green Wafer like Bridge Rectifier?

Well, I do not know who made that bridge but wafer style bridges (one hole in the center) are made by a huge variety of companies in the world. One of then that I know of is NTE. The amplifier in question being old (by now) it is kind of… unlikely that you would a brand new one made by the same people (but….you never know!) However to “purely fix stuff” like this you don’t necessarily need to aim for the exact same form factor or manufacturer. After all is just a simple (High Amps) Bridge rectifier. As long as you find another one having the same or better specs and can mechanically be fixed to the same position in the same hole you should be more than safe to do it.