Q.Can we grow calla lily from cutting of a stem?
Where can I get the bulbs for these also?

Cuttings from the flower stem won't root. The easiest way to propagate calla lily is by dividing the tuber that grows under the soil. There will be offsets, new developing tubers that have a center "eye". Cut these off and pot them up. Every major flower company and nursery offers calla lily. Due to hybridization, they now come in a variety of colors and some have speckled leaves. The following link takes you to an entire series of articles on growing, fertilizing and dividing calla lily.
https://www.gardeningknowhow.com/search?q=calla%20lily