It depends on where you are and what the specific case facts are.
A few states have groups where funds have been established. Depending on the facts and circumstances of the individual case organizations such as ACLU, NRA, SAF, JPFO and others may become ibvolved with personnel and/or funds. Individuals may donate funds for a specific case.
There is no "insurance" that will provide funding for civil suits, as those are cases which generate "profits". There are a few legal services groups out there that offer "insurance" that pays for legal representation in the event of criminal charges - go Google them.