You seem to have a specialisation which would be in demand.
In my experience the key to success in freelancing is sales ability. You need to find customers who could benefit from your expertise. When you get to meet them you need to demonstrate the value you bring to them. Having sold them, your technical skills are used to deliver and then you need to collect the money.
A portfolio and/or references are useful in establishing credibility. I would suggest having a "sampler" app running on a tablet to showcase the "solution" that you can deliver. I find successful test drives help the sales process along more than anything else I've tried. Even if what you showcase is only marginally relevant, it often still is sufficient to start the requirements elicitation process. That is, find the need and show how you can satisfy it.
