I am looking for this plant! If ANYONE has it please get in touch with me. Thanks. I will paypal you for it no questions asked. I will want a photo to know you have the right plant however.
Althaea officinalis - this is the one colonists used the roots of to make the confection marshmallow. It orginated in Eurpoe and grows in Salt Marshes.
Those species are common terrestrial garden plants. You should check with your local nursery to see if they have any. It's probably your best bet. I would hazard a guess that only the most die-hard native plant nut would have some in an aquarium.
WTB Marsh Mallow 
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