Have you contacted Omnisource? Might be able to work out a deal that they can have them for free if guaranteed to be shredded. Give them a sealed box, they'll toss the whole box in the shredder/separator.
I had a rig all imagined in my mind, including an enclosure to hold the drive and capture ALL the shavings, even with the shop vac exhausting outside. Then I realized I was appearing to overthink/overengineer.
All my old Hardrives get a 45acp to the face. It kills their soul I hear.
5 gallon plastic bucket and muriatic acid in a well ventilated area.