I have Water Hyacinth I can send you for postage but it will be about 2 weeks because I just thinned them out.. If your interested email me

Flag iris is a good bet for zone 5, I used to plant them in dirt before winter, but last year I left them in the pond through the winter and they were fine. I can split some of those if you would like some. I don't know where you're at in zone 5, we're near Youngstown, Ohio. As far as the water lily- I've had success for 3 years now by overwintering them in a bucket of water in the basement in a dark spot. I take them out of the pond once it starts to freeze, and then usually place it back in the pond after Memorial Day.
Water hyacinths are another good choice for zone 5, but they can take over and spread like crazy. I no longer have those.