If you don't want to do it yourself, email [email protected] to explain why you're sending media and to coordinate logistics. You'd mail the discs to the Internet Archive's physical address [1] in San Francisco, ideally with the Internet Archive item identifier (https://archive.org/details/{$ID}) associated with each disc noted on the disc (post it note or similar, not an adhesive label). Should cost only a few bucks to send it USPS. They will preserve the donated media in their physical archive located offsite.

[1] https://help.archive.org/help/how-do-i-make-a-physical-donat...