contact your breed specific clubs for reputable breeders
http://www.gsdbreedcouncil.co.uk/memclub.phpsearch through their members clubs and you'll find one in your area
Just to let you know, you may find it a little difficult finding a pup around the xmas period as most breeders try not to have litters at this time due to the obvious
good luck
hope you find the little one your looking for