We are interested in getting our first dog, and are looking for a young boxer. I would really like to get a dog that is still young (under 1 year) but old enough that it is physically able to be house trained and sleep through the night. I have had dogs all my life, but my husband hasn't and I just know that although he is very willing to spent time exercising, training, and loving a dog, his patience has limits when it comes to biological messes and sleepless nights.

I don't want our first dog to cause my husband to get a bad attitude about them, because eventually I want to have more.
I have been looking on Petfinder and have emailed for information twice, but both boxers have been adopted (I'm happy for them!) by someone else. I really would prefer to go with a reputable breeder that has done the medical checks. However, I haven't found any nearby and I'm not really sure even how getting a dog from a breeder works. My questions are:
Do you just find a breeder you like based on browsing the 'net and contact them about future pups and put a 'bid' in for a future pup?
Will breeders keep puppies until they are a bit older?
I hope I've put this question in the right forum...thank you for any advice you can offer!