Your local brew shop should have those by the case. They're not cheap, but they're worth it. Make sure you get extra rubber seals.
We've found that about 4 ounces of priming sugar (roughly 1/4 cup) per 5 gallons gives a nice carbonation. Make sure you dissolve it well in about 1-1/2 cups of water. Then add it to the finished beer before you bottle it.
We've had a lot of good luck with the 'kits' that come in a small carboard box. Work your way through a couple of those and you'll be ready to make your own recipes.
bttt