Start a development agency and advertise where non-tech people would look for you. Yellow pages, facebook page, fill out your details so they show up on google maps.

You'll have a ton of businesses contacting you looking to have their ancient specialised software replaced or improved upon. They wont have a budget to make doing it just for them worthwhile, but it will be a fountain of SaaS ideas that come with built in validation and a first customer to learn the specifics from and act as a reference.