New Mexico tea co. has a cardamom black tea.
As a couple of people have pointed out, it’s so easy to make your own cardamon tea at home. It’s quite popular in Iranian homes, or so I gathered from the couple of Iranian flatmates I have had over the years. Try adding two bruised green cardamon pods – crushed a spoon or between a chopping board and a kitchen counter should be sufficient to release the oils – and one or two dried rosebuds to your tea as you pour the hot water. For a stronger flavour, simmer two bruised cardamon pods in one cup of water and two or three tablespoons of sugar until a thick syrup is formed, remove from the heat, top up the hot water to fill a cup and add your tea of choice. It goes well with Ceylon teas.
Otherwise, Mlesna (also known as Metropolitan Tea Company) has a cardamon tea which comes in a really nice wooden box. From memory, it is just tea and cardamon.
Hope that helps.