Ariadne, we bought quite a mature wisteria, very unusual, sorry can't remember the variety off the top of my head, but it's white and the flowers erupt before the leaves grow. Essentially, it is covered in pure white flowers and then when they start to fade the leaves quickly replace them.
Ours flowered the first year it was planted but it was quite tall. I suspect you can buy with flowers on, now would be the time to check. Why don't you call a garden centre and ask them. x