Turkey is the largest producer (2/3 of the global supply), and is accessible without import fees due to customs union with the EU, so it can't be replaced easily.
With Ferrero purchasing a quarter of the world's hazelnuts, and Turkey producing 650k tonnes, which is about 2/3rds of the world, that means that even if Ferrero was already sourcing from different countries, that means dropping Turkey as a source would leave Ferrero with a total purchase of about 230 tonnes.
With Georgia producing about 37k tonnes, they'd need to buy everything and also the entire US and European supply. In practice, they'll probably already be purchasing from those countries so they'd need to seek out even more sources, maybe build their own overseas farms to compensate.
There is no real alternative to importing from Turkey.