This is pure guess work based on nothing except your description and where you bought it, but most likely you are talking about a rhododendron rather than what is meant by azalea in the horticultural sense. The species impeditum would fit your description, is hardy enough for NH, and was pretty widely available at nurseries years ago. The hybrids Purple Gem and Ramapo are other possibilities. There are good photos of all three at www.hirsutum.info See if one of these corresponds with your memory.