I am looking for plants or seed of the plant commonly called Tufted Loosestrife. It is a more northern species tha I want to try and grown in my Z-6 mountain bog.
Check Prairie Moon. Quite sure they offer this species. I'd say you have reasonably good chance of success with your wet site. Not a good one for very hot locations though....but again, the wetness of your site should be amenable.
Prairie moon does have it. They say bare-root plants ship in April. They also have packets of seed, although with this species a single plant would probably be all you need. It spreads via rhizomes.