First, sorry for your loss. I know it might sound cheesy, but I think it’s the best way to start this conversation.
Here’s my advice:
1) There is always Ebay. As crummy as it has become, it still could be the best way to find buyers who want the retro stuff you want to sell.
2) Go into YouTube and search for channels that talk about retro games. Maybe get in contact with those channels to either offer what you have or get their advice for selling. Channels dedicated to retro gaming are likely to have the answers you are looking for.
Hope this helps.