You can obtain an insurance policy with a SR-22 without a car.  Just ask your agent for a non-owner policy.  A non-owner policy covers you for liability on any car you drive.  To qualify for the non-owner policy you cannot be a registered owner on a car.

Once you obtain the policy the insurance company will either provide you with a paper SR-22 or they will electronically file it for you.  You will need to tell your agent how you want this done.  If you are going to the California Department of Motor Vehicles to re-instate your license you will want to take the paper SR-22 with you.

In any event, consult your agent.