Allium roseum is a lovely thing, but I haven't risked it in the garden, I suspect like A.triquetrum it is ineradicable!
This one is Babbington's leek and is a form of the wild leek progenitor Allium ampeloprasum. Both it and roseum have bulbils in between the flowers.
Like the 'Jacks' gladiolus it is now known to be a clonal hexaploid and therefore of very low fertility if selfed, behaving in gamete production like a functional triploid so the chromosomes don't pair off properly.
It used to be called Allium ampeloprasum var babingtonii, but although it isn't published I think it has to be a cultivar now. That would make it Allium ampeloprasum 'Babingtonii'.
When it was thought to be a subspecies or variety it was 'endemic' to The British Isles [Cornwall, Eire and The Chanel Islands].
I think current opinion is that it is an escape from monastic gardens.
Certainly the bulbils are useful in the kitchen as a mild Allium flavour in cooking.
I agree with your customers, getting hold of 'Whistling Jacks' means avoiding the dutch suppliers. It took me several goes and finally I bought a pot in flower to be sure I had the right thing. Thankfully it bulks up rapidly, which reminds me it is time to lift and spread it around the garden a bit.
The next one is a hardy [at least here] perennial.
Chad