If you are interested in herbs for relaxation, I would recommend lavender and chamomile. Both are very calming and soothing.
Lavender is a very popular herb for lotions, oils, incense, bubble bath, body wash, scented candles, etc. The only place I know of that has it in tea form (at least where I could buy it in my area) is Teavana.com Tevana specializes in various types of teas. They tend to be pricy but the quality of their products is wonderful.
You could also try growing your own or look for it at a health-food store or an occult shop, if you have any near you.
Chamomile is a very easy tea to find and is sold in most grocery stores. Lipton has an herbal tea sampler pack, chamomile being one of the included teas, or you could buy a box of just the chamomile. I do believe that Lipton sells both options.