Call it what you want, Ipomoea Aquatica, Kang Kong, Water Spinach, Rau Muong, Ong Choy etc. It is all the same plant. It is an aquatic plant in the sweet potato family and it is delicious for both its greens and its stems if harvested before they get to thick.
Sources of seeds, if they are out just search either etsy or ebay for Ipomoea Aquatica for the most reliable results.
Etsy – https://www.etsy.com/listing/1241510870/1000-water-spinach-seeds-rau-muong
Ebay (I have bought from this seller) https://www.ebay.com/itm/325134730891?hash=item4bb38a468b:g:T4MAAOSwH3xhDCxL
