I don't think it's too difficult to find such opportunities if you're willing to be a freelancer/consultant.

I've gone for periods at as little as 5 hours a week. In that case I was mentoring more junior programmers, rather than owning a software project myself. It worked out great and the client was happy.

As you saw, at 16 hours you can easily own a software project and get great results. There's no reason you can't bid for freelance work at that level of commitment.