So, a while back I found the chorus section of my Opus 3 going tits-up. The effect itself is diminished, ruining my precious, Solina-slaying string machine! I pointed a local tech to the chorus modulation board and he found two out of three of the BBD ICs on it dead.
Here’s the rub: the BBD in question is an SAD512D, which hasn’t been manufactured in years and is infuriating to try and find. These did come in other, by now equally rare items like certain effects pedals and electronic organs. I scour ebay and the cheesy-home-organ sction of Value Village to no avail. And I need TWO of them! And even once I do find them, they too will inevitably fail, as will the third one, maybe not soon, but someday. 
Can anyone point me toward finding this chip? Or, to you techs and engineers, does anyone know of a suitable replacement or workaround?
My humble thanks…