An SR-22 insurance policy is generally a motor vehicle liability insurance policy required for reinstatement after your drivers license has been suspended or revoked. SR-22 insurance is uniquely suited for these situations, because it requires the insurance company to notify the department of motor vehicles if the policy is canceled, terminated, or lapses. If any of these things happen, your license will typically be suspended until the policy is brought current or reinstated. Under the laws of most states, you must carry SR-22 insurance for a certain period (often three years) after the end of your suspension or revocation.
You can not buy a separate policy for an SR-22 if you already have an insurance policy. You will need to cancel your current policy if your insurance company doesn't offer an SR-22 and purchase a policy with an insurance company that does. You can get an SR-22 insurance quote here.