If you are looking for an adult, you might want to look at a rescue. There are many purebred GSDs in rescues. Breed-specific rescues are great because the dogs are usually living in a foster home and therefore are most likely housebroken, and you know how they get along with other dogs, cats, kids, other people, etc. The rescue can help match you to a dog that fits your lifestyle too.
ADCH Mikko (USDAA) SCH-B; (NADAC) EAC, EJC, TN-E, TG-E, VerO; (AKC) NAJ, CGC; (NACSW) NW1 - 9 year old GSD