I'm in a similar position, done my share of audit and transaction advisory work, got my CFA charter and never had anything to do with taxes. Finding a side hustle in this field is not easy.
However, there are plenty of low-cost or even free data vendors out there (I like e.g. Quandl, Calcbench and Intrinio). I enjoy viewing the data like some puzzle: there are a myriad of pieces, I just need to come up with a creative way of combining them to create a new, possibly useful product for others (other auditors, analysts, investors, students, ...) - be it a mobile app, a web service, or something else. You need to be a bit tech savvy of course.
Sorry, that's about as specific an advice as I can offer :)