If you want a pure bred Maine Coon kitten and you are willing to pay for it, then the first thing you need to do is to NOT hit up the pet shop. No responsible breeder would place their kittens in a pet shop for sale. The next thing you need to do is some research.
Check with the CFA for local catteries that are registered breeders. You can check with the local Maine Coon clubs or national clubs to find a responsible breeder to purchase your cat from. Any breeder that is responsible will belong to the CFA.
Any breeder that is responsible will answer your questions and will very likely show their cats. You do want to choose a local breeder if you can because shipping the kitten can be very expensive and it can also stress the kitten out.
Things to Ask
Once you have found a breeder there is a list of questions that you should ask and that they should be very willing to answer. Ask if the cats have been genetically tested for HCM. Ask if they show their cats. Ask about the line or heritage of the cats.
Ask to see the parents. Ask to see where they are sheltered. Ask to see health records. Any breeder that is interested in making sure that their kittens wind up in good homes will be happy to see that you are interested in their heritage and their care.
The goal is to always make sure that you are dealing with a breeder that puts the cats before profits. Maine Coon cat breeding is not a for profit business in most cases. The cats are bred for either show or for pets. Typically the breeder will keep the kittens that they believe are show quality and sell the kittens they believe are pet quality.
The difference between the two groups is very difficult to discern. It may be something as simple as the eye shape being a bit different or a patch of white is not in a perfect triangle.
Saving Some Money
Typically if you buy a Maine Coon as a pet it will be less expensive than purchasing one for show. It is also usually an added expense to get the breeding rights for a kitten. The breeding rights can cost you about $2,000 on top of the cost of the kitten which can also be around $2,000.