Get rid of qualified immunity and make police buy insurance. Not that hard of a fix
Why should good cops subsidise corrupt cops (with a hefty overhead for the insurance companies)? Doesn't that create an additional incentive to be corrupt? Many people are more sensitive to punishment than reward: I'd expect having your premiums go up because a fellow officer got done for abusive conduct would feel like arbitrary group punishment.
Teachers buy school supplies, tradesmen buy their own tools, police can buy insurance.