I am very sorry for your loss.
Why don't you contact some of your son's friends and see if they have recordings? I don't know how old he was, but young people these days record all kinds of things. You may be able to turn something up. You could go through the address book/contacts on his phone (those should still be saved) and call or text people. Best of luck.
This is a good idea. I kept a voicemail from a friend for years after he passed. Several of my friends did as well. How old was your son? Was he in school plays? Team sports? I bet other parents have videos they could share.