Seat belts can be installed in any golf cart for a very nominal cost. Less then $50 for two. Takes about 15 minutes. They come in many colors, with all the necessary hardware and backing plates. all you need is a drill and basic wrenches. Here is one link where you can buy them. I am sure there are others and probably places like Autozone or Pep Boys have them as well. These are lap belts only. I am sure sholder belts can also be installed in any cart with a roof by attaching to the back roof support posts, but have never tried that.
http://www.gotbelts.com/style.html