It's difficult to find quality GSD's. I'd suggest you to attend dog shows in your city, check the varieties in the event, speak personally with the breeders, take their contact details. If they have litter available, they should let you know or they'll let you know when the next litter will be available. In some shows, the breeders even exhibit the puppies in the shows.
Or, you can get some contact details from a reputated vet. You should personally visit the kennel, ensuring the dogs are kept in clean environment, females are healthy looking, etc.