Aren't these sold in Holland? A friend gave me some bulbs this spring and they bloomed well for me. According to him, they increase at a fast rate and are easy to grow. I just dug mine up because they're not hardy in this zone.

I buy them whenever I find them offered. They are always imported from Holland, but only two species have been available, a yellow called Sulphur Queen and a white one. Al

Ton....
Are you seeking the North American species?
If so, seed is rarely available and thus, very expensive. The last offering of Hymenocallis occidentalis (caroliniana) seed that I saw was $5.00 USD per seed!
Bulbs are sometimes available from nurseries specializing in NA Native plants, but I suspect they are harvested from the wild.
I recently purchased Hymenocallis rotata (traubii) from a TC Lab in Minnesota, but they only sell in tray quanities of 72. You can combine other perennials to fill a tray, but minimum quanity of each is one cell pack, containing 9 plants.
Hymenocallis caribaea and littoralis, both tropical species, are often available, but must be grown in a TGH, when temperatures fall below 5 Deg.C.
Most gardeners here view them as difficult to maintain, because of the constant moisture requirement and opt for the S American species, which are cheap and readily available.
Rb

Ton, Most species are rarely available as said above. I was fortunate enough to get some large flowering size H. speciosa earlier this year and when they flowered it was stunning. I know of one place on line that offers them if you e-mail me directly (I try not to advertise for people on-line). They have the H. rotata for example as flowering size bulbs and also some smaller ones. They also have many other species and some F1 hybrids. Best of luck :o) Dan