Heirlooms are varieties that have been around for generations, and developed through selective breeding rather than hybridization or genetic modification. Some have natural resistances to diseases or pests, and all produce seeds true to the plant if proper care is taken to avoid cross-pollination. For example, if you save seeds from your Black Calypso beans, they will grow more Black Calypso beans. This is not true for "hybrid" varieties, which may not produce fertile seeds, and if they do they may not produce that same plant, but a previous "parent" cultivar.
Most of the heirloom vegetable seeds we have were purchased from Big John Lipscomb. Some plants were purchased at the Sunshine Garden Plant Sale in Austin. Others were bought elsewhere.
Sunshine Community Garden - Austin, TX