I got no idea but why dont u just use regular tea and brew in billy can while camping and chuck in a few fresh young eucalypt leaves for authentic billy tea or do similar while at home.
I Remember The Beautiful Tin "Tea Caddy", It Originally Came In.. Still Have One Or Two In My Shearing Shed Somewhere. At Shearing Time......Billy Tea Was Just As Important To The Shearers As The Sheep Were..... Cheers Glen.