Hexamine is, basically, seriously "de-rated" explosive, apparently related to RDX, which may explain its heat-generating capacity.
The early Oz stuff was made at the old Explosives Factory, Maribyrnong. Later production seems to have come from ADI St. Marys.
Amusingly enough, one of my later-serving contacts tells me there was some supplied by the wonderfully-named, "Far Side Marketing" (Gary Larson joke?), in Turvey, Bedford, England, with the actual manufacturer not stated,.
Full name: Hexamethylene Tetramine. U.N. No. 1328.
It is interesting stuff as, when it burns there is NO liquid phase; straight from solid to gas. This makes it "relatively safe" in field use.