Literature may list the genus Corydalis in either the Poppy or Fumitory Family, with most of my books saying Fumariaceae. Over three hundred annual and perennial species grow in the Northern Temperate Zone. Central Asia and Western China, along with some in South Africa, have the heaviest concentrations. Only the perennial species are of interest here, still leaving a wide list of plants to choose from for the garden. The genus has probably not gained in popularity any more than it has to do due to difficulty in propagation.
Germination is generally erratic.
Corydalis may have tubers or rhizomes and resent disturbance when very young. Either sow them in the desired location or thinly plant in pots where they can grow on for the first year before transplanting. Having gone on about all the difficulties of finding plants or seed, the germination or propagation, it should also be emphasized that all is worth the efforts. Corydalis will perform well where few other perennials survive. Once established they do generally seed themselves about in the garden.