The retainers are made based on your impressions, from which the casts or molds for your teeth and the consequent treatment plans are made. This is an expensive, pain-staking, and time consuming process. At this time, it will not be cost effective for you to just have retainers made without getting the whole aligner treatment. If you had braces with a previous orthodontist, we suggest you go back to that person and see about getting new retainers.