Where people get tea and what kind the drink

1. Health food stores, asian food stores ( if you are near a city that has a Chinese section, that is awesome) or try  Asian Grocer.com.,they have a good selection of real Asian foods.
2. i buy my green tea at a authentic japenese/sushi rest. sent right over from japan. if you have one near you they should sell you a bag
3. I'm a tea nut -- preferring oolongs, puerhs and green tea. I have experience with some of the online vendors mentioned above -- In Pursuit of Tea, Teance, Imperial Tea Court, and O-Cha.com -- and I think those are good choices. I personally have not had such great green tea from Ten Ren (their focus is oolong). You will do much better with tea specialists (online or brick/mortar) than supermarkets or even Asian groceries. If you are in or near NYC, I can also recommend highly The Tea Gallery in Chinatown. If you like Japanese greens, also try sencha.com; they often have an astonishing variety!
4. I had been a regular shopper at Upton Tea online for their sencha, but I've converted to My Green Tea. Though the name isn't inspiring, its sencha is the best I've tasted. They sell at retail in a handful of stores in the greater Seattle area and online at mygreentea.com. Their bagged sencha is fresher and more complex than most other loose green teas, and their loose sencha is heaven -- smooth to the point of buttery.
5. I'm adore green tea and am very picky regarding taste and aroma. I only use loose leaf teas that I pick up from asian and boutique tea shops. I don't buy on-line because I want to see and smell the leaves... but I'll link some pictures so you know what you are looking for. 
6. Here's a link to a really good web tea vendor. Their green teas are excellent and their website offers lots of info. And if you're ever in San Francisco, you can visit their shops in Chinatown and in The Ferry Building Marketplace.Link: http://www.imperialtea.com
7. Maeda-en is a pretty reliable Japanese brand that I've seen in Japanese and Korean stores. I generally buy Japanese tea, but friends tell me that Ten Ren(Chinese) is also good. I've seen that in both Vietnamese and Chinese stores.
8. I agree with Morton about bagged tea and I'm glad he suggested that you can buy the empty bags and fill they yourself. Once you start drinking green tea, none of the prebagged tea tastes like much of anything. 
   Another nice tea source is Far Leaves Tea. Although it is not a green tea, the blood orange made with fresh blood oranges is amazing.