Sorry for the late reply,

Other companies and institutional investors acquire any public shares over time. We do not force the sale of those shares because of exploitable behavior by players over the years.

Share Holders will occasionally sell shares, especially during times of economic crisis. You can have the game notify you via the memo system by clicking the checkbox next to the outstanding shares. (#2 in this picture) https://wiki.gearcity.info/doku.php?id=gamemanual:howto_stockmarket#stock_window

In our expansion crowdfunding efforts, we have several tickets that will open up the stock system again, including these bounties:
https://www.ventdev.com/forums/showthread.php?tid=3885

https://www.ventdev.com/forums/showthread.php?tid=3886

https://www.ventdev.com/forums/showthread.php?tid=4065

You can find more information on our Feature Bounty System here: http://www.ventdev.com/fbs/index.html