what remote goes with this astroflex unit

I am looking for a remote for this unit. A person was referred to me after a shop thought the remote start in his truck was a Crimestopper. He bought the truck used and found out later that it had a remote starter. Of course, he didn't have the remote. I am not an Astro dealer, so I have no idea what model this could be. All of the searching I have done has resulted in nothing.

Here are some more pictures of the front. The unit was still hooked up to the vehicle.

The unit in question is an Astrostart 5204U. It is a two way unit (may have an alarm as this model came with siren etc).  The remote you are looking for is part # 310-052-451. Note that a remote for a 4204U will also work.