Melissas.com, Amazon.com and FreshDirect.com sell purple potatoes online. The selections include well-known cultivars, such as purple majesty, as well as purple versions of more common potatoes, such as purple sweet potatoes and purple fingerling.
The available online inventory of purple potatoes is extremely diverse but spread out across many vendors. As of 2015, Melissas.com carries 3-pound packs of baby purple potatoes for roughly $16, while Amazon.com features purple sweet potatoes and purple fingerling potatoes for roughly $19 per 2-pound bag and $108 per 10-pound case, respectively.
FreshDirect.com specifically carries the Stokes purple sweet potato, which is a patented heirloom. Other heirloom and heritage varieties, such as lion's paw, are typically available randomly at local farmer's markets or as seed potatoes through garden supply stores, such as GardenHarvestSupply.com.