Breeder Listings
Here at Boxerworld we have a page with breeders that do the recomended Health Testing for thier Country/Region of the world

You can find many US and a few Canadian breeders
http://www.boxerworld.com/breeders/ If the breeder of your choice does not have any pups at this time you can then ask them for any other breeders in the area that they may recomend (since we are still building our refferals). If you have any luck let them know about Boxerworld and tell them we would love to add All Good Breeders to our pages! :D
And remeber that a Good Breeder will most likely have a waiting list for pups since many do not breed often. You may wish to consider rescue if you decide you don't want to go the puppy route again, many BW Members decided that 1 puppy was enough!
http://boxerworld.com/links/Boxer_Rescue/USA/
Read the Breeder page that will give you a good start on what to look for

Keep us updated and feel free to ask more questions on what to look for in a Breeder.