I don't know if this helps or not, but solidago is another name for goldenrod, the perennial. Are you looking for the plant or for the cut flowers?

I'm looking to grow them...for arrangements!! Hopefully!

Don't overlook the wild Solidago. There are various types so be selective and pick the types that meet your design needs. I have several on my property and choose the ones that have an upright, triangular shape. It helps greatly with establishing a line in the design, plus lasts forever. I think the key is to pick it before it turns gold. I cut them when still yellow-green which is a real neutral color and is a nice filler. I sometimes even sell it to florists.
Several years ago when I went to a wholesale florist I first spoke with him on the phone and asked about several things I had available. When I asked about goldenrod, he basically said, "No way." Later, when I took him stuff to look at and tell me what he thought about quality without pushing at all for him to buy anything, his last words were the most important. "I'll buy everything you have on the truck." He didn't even recognize the goldenrod since it was not mature, but he must have liked the form and neutral color. Now I call it Solidago, its formal name so that it doesn't scare people away.
And to answer your question, a good nursery should have the Solidago you are looking for.
Ann