I recently joined a large tech company, and so most of my mentoring has been within the company (including other departments though). One thing that I did more of previously was sign up for different events at the university I went to grad school (which happens to be in the same city I work). It's pretty low risk, in that you can commit to an event one evening without needing to commit to anything specific for the long term. They also usually have different formats for events so you can pick something you feel you can help more with.
