If the part that broke is the bar pin (the part with the U cut on each end that goes through the top shock bushing), then you'll need to replace the shock because the bar pin comes with the shock. And you'll need to get two shocks because you should never just replace one shock. The bolt you can get from any real hardware store. While you're at it, replace both and make sure they're either grade 5 or 8.
Driving with a shock missing is doable, but you should be careful. Your rear will bounce a lot more and you'll need to watch yourself real carefully on turns.
Also, and this might be why your bar pin broke in the first place, you need to make sure your shocks are the right length for your lift and you have sufficient bumpstops to prevent the shock from being overcompressed - otherwise you'll just break your bar pin again when you compress your rear.
The top and doors on this vehicle are designed only for protection against the elements. Do not rely on the top and doors to contain occupants within the vehicle or to protect against injury during an accident. Wear seatbelts at all times.