I have a bookmark somewhere for using heat-shrink foam like stuff which someone used for making LOTR and other armor plating, I'll try and find it again for you. and there was another guide using surf-board material to make Zabuza's sword from Naruto, which looks almost the same size as the sword you want. I'll try find that one for you too
I Larp. Look it up on google or you tube if you wnaan know what its about. but regardless you need to make weapons and armour for it. So here is what i have learned from doing tests and such
for weapons i recomened using Pvc piping for the core, with a respective thickness. Then for the shape of the foam, you can try to cut out pre set foam but i dont recomend this. you should make a mold, out of clay, metal, card, wood, anythign that retains the shape you want. Then buy some liquid laytex normally about 5.99$ for 3 litres, then add some thickener. Once its set use spray paints.
If you want help on a particuler iteam dont threat to contact me as the above is a real general overlook on how to do it.