This site is great for GSD's, they have lots of rescues of all ages and can give really good advice about the breed:
http://s10.zetaboards.com/biggsd/index/
Please, please do research into the breed before getting one. If the dogs you have seen are for sale then be very wary. I would want to know why a 5 month pup is for sale. They could have alot of problems either problem behaviour or medical problems. GSD's can have alot of hereditary problems, epilepsy, HD etc.
If you are first time dog owners then I would really urge you to join the above site and have a good read through it (including the training and behaviour section).