What about former customers, peers you met at trade shows etc, ex employees who moved onto big things, former investors, etc. Most business owners form a network over the years whether they work to cultivate it or not.
Customers are a little tricky, needs to be handled with care. Trade show contacts and ex-employees and former investors, board members are all good people to contact. But you may have message the fact that you are shutting down the business first. Also if you had co-workers from a job you did before your started, reach out to them. Many of them may be VPs and CEOs by now, and would value you as a coworker.