Is this your first snake? If so then I'd suggest a reptile show as the best option because you can see lots of animals, handle them, ask questions of the vendors, pick up any supply items you might need, pick up some food for your snake, etc...
If you know exactly what you want an online breeder/Morphmarket is a good option too. A local pet store is seldom a very good option unless it's a reptile-specific store.