Organisations which help victims, offenders and their families require funds. Many do not receive core funding from government and rely on the goodwill and generosity of charitable trusts, and foundations, and members of the public. If you don't feel able to be involved in any of the direct forms of volunteering, and fundraising is your "thing", you are likely to be welcomed warmly, especially if you have innovative ideas for persuading people to part with their money, as well as the traditional sponsored activities, raffles, bring-and-buy and car boot sales.
However, you should not undertake to raise funds on behalf of a particular group without the express permission and authorisation of the group. Criminal Justice is an area of work which does provoke some strong reactions; eliciting donations to help fund a nightshelter for homeless ex-offenders is unlikely to be as easy as getting people to give a contribution for a home for stray cats!