Kuana Torres Kahele says not having blooms is no excuse
just use any bouquet from your grocery store, or any flowers, or other materials at all that are available to you.
I am of course very partial to Plumeria but made a Bougainvillea lei in January when there were no Plumeria blooms available. I have made several different styles of leis. I recently bought several books on lei making and am practicing new techniques (as I did today) when I have time.
Here is an example of a beautiful lei made entirely with leaves.