Ask HN: Where to buy real SAAS business?

So we have Flippa, bizbuysell.com, bizquest.com etc. These are selling mostly low end, affiliate marketing types sites. If someone is interested in buying a real SAAS/software business, where can they look ? By real, I mean selling an actual product with paying customers.

I understand that most people do not want to list their business for sale due to fear such as competition etc. I also understand that owners do not want to sell if they are profitable but there is that small group of owners who have a profitable business but want/need to sell due to a number of reasons. May be they want to work on their next big thing? Howver, they keep quiet because they don't know where to find buyers who are genuine and real. But is there a way to find these business owners ? I am interested in exploring an opportunity to buy an existing saas/software business that has net cashflow of about 5K per month (not revenue). how to find these ? Btw, contact is in my profile if you want to talk.