Yes, as tech workers, we have the ability to use our valuable skills pro bono. But I think it can also be beneficial to step out of the tech bubble and integrate with the rest of non-tech society on non-tech terms. Most of my volunteer work has been with students--when the topic comes up, I get to tell them all about why they should consider pursuing programming as a career.
Most of my volunteer work has been obtained just by walking up to the people involved and asking if they need a volunteer. I don't think you need to look for a formal volunteer program.