I dont think you can. Unlike the USA, where you can buy the MLS jackets through OSI, FIFA and UEFA only give that stuff to the officials working those competitions. There are many stories of fairly senior referees in Europe getting into SERIOUS trouble because they were seen wearing a Champions League or UEFA Cup jacket or shirt that they had not been given. It's frowned upon BIG TIME !
Try refereeworld at www.refereeworld.com They price ref gear resonably, but the shipping is pricy. They probably have the track suit, but it likely won't say UEFA on it.