Some folks collect old stock and bond certificates. This is called scripophily.
Some stock certificates that are worthless as securities may have value as collectibles because of:
You can find collectors and dealers in such sources as eBay, or local antique dealers, especially ones who specialize in old currency, stamps, or coins.
People buy and sell stock certificates on popular websites such as eBay and Etsy. In fact a whole community has developed around this hobby.