
Hi Ruth, welcome to Champdogs!
i'm sure someone who is much better than me at doing links will be along in a bit, but a couple of things to make sure of when you are looking for a puupy are to make sure both parents have had all of the relevant helth tests for the breed, and also that their health test scores are well within the normal range for the breed.
Also, try to contact the breed club as well, they may be able to point you in the direction of reputable breeders and will be able to advise on what helth test should be carried out.
The Northern Boxer Club contact is Mrs V Van-Beck. Tel No: 07836 325125, according to the Kennel Club website.
Good luck with your search for a puppy - come back and let us know how you get on

Claire