I’ve personally had around a 1:30 success rate in sourcing scrap wafers for non-customer related projects. Various issues make sourcing exotic wafers difficult. The #1 problem with contract bumping houses is that they are generally tied to contracts which require them to either return scrap or destroy it. This rule is intended to protect intellectual property.
The next hurdle is finding a potential supplier while they have the scrap on hand. If they tell you “I’ll let you know when we have some extras on hand”, I wouldn’t hold your breath.
Another roadblock is cost. Some scrap wafers and new wafers actually have similar price tags! Call me old fashion, but scrap wafers should be a low cost option for those of us who don’t need the integrated circuitry.
But if you’re still looking to sell scrap wafers, or if you can donate your wafers, I will take them off your hands and make sure they go to a good cause.