You could save seed; that would take about 2 - 3 years for bloom. Perhaps the fastest method would be dividing the bulbs. You cut the bulb into sections making certain that each piece has part of the base and plant them. From your photos them seem quite content with their present conditions.

Another method would be to dig the bulbs and remove any offsets (baby bulbs) from the Mother plant and plant these.
Most alliums are not too demanding and a yearly application of a time release fertizer early in the year would be all they would need. As soon as the flowers fade, cut them off so the leaves can use all their energy on developing the bulb and not for seed production. They will bloom better next year.

These bulbs enlarge every year and after 3 or 4 years the bulbs divide on their own and you will have several more blooms coming up in different spots. I have dug them up and spread them out, but I don't know that you have to. If you want a straight row, however, you will have to dig them up and respot them because they spread in more of a circle. If they are Globemaster, they multiply very well for me. I mark where they are and after foliage is spent, respot them midsummer.