What is your goal?
Is this to satisfy your own creative / contributory impulses, help others, aid in specific areas, ???
What time commitment are you willing to make? How fixed or flexible should the schedule be, for both you and the volunteer activity?
Are you interested in a strictly volunteer situation, or something which might more resemble an intern / apprenticeship engagement with a transition to paid work on a part- or full-time basis?
What kinds of work / projects / organisations will you NOT work on?
Keep in mind that one engagement can often lead to another. For data analysis, specifically, there's often a three-way mismatch between analyst capabilities, client desires (both expressed and unexpressed), and actually viable value of available data. There's a certain romance in working for a naive or challenged client (e.g., many NGOs or community organisations) which tends to fade under the harsh light of reality (painfully constrained budgets, limits to the benefits of data analysis itself, etc.).
That said: reaching out to local organisations, educational institutions, government organisations, etc., might give some interesting leads. There are groups such as VolunteerMatch, though they tend overwhelmingly to be oriented to both nontechnical and often corporate-charity type engagements.
I'd strongly suggest looking into local continuing education through a community college or your region's equivalent. Both the course material and contacts should help concretise both your own goals and local opportunities.
