We picked up one of these for free off Facebook Marketplace.
Ryobi does not list replacement blades for this model.
And that’s ok, because you can find replacement blades easily on eBay.
(search for “Eco ES1600” or “McCulloch MCS2001 XL” or “08-08-62”).
It’s not the blades though, it’s the bolts that are the problem.
Ryobi recommend they you replace the bolts every time you replace the blades. Over time, the 6mm hex bolt socket wears, which means eventually you’ll need to get new bolts.
Ryobi do sell a newer shredder model, the RSH2445B, and they do sell blade sets for that model. So I took a gamble and ordered a set of Ryobi RAC1110 shredder blades from Bunnings.
(don’t buy them from eBay, you will pay 3 times the price)