
Guest I don't understand why you would need to purchase a dog for your purpose, after all once it had produced your litter it would be no longer of any use for that purpose and you would have an extra dog (you might want to keep a male pup)?
For the price of a puppy (and in many breeds for less) you can have the use of the best stud dogs in the country. All you need to do is comply with the requirements that a reputable stud dog owner would have, which are only those you should be willing to do.
Your bitch should be assessed as to her quality (even the best stud can't produce silk purses from sows ears) be Hip Scored with a good result, have any other breed specific health tests (I forget the name, but there is a serious condition of the skin structures) and of course she should be of impeccable temperament.
I suggest you contact the breed club/s and join. Attend some shows to have a look at the dogs available and the quality of their offspring.
Good luck with your research.