Edit: more specifically, DEWAT is a 'de-activated weapon'. As in any weapon that used to fire actual rounds, but is now unable to do so. The ATF has their code for it, and a quick search revealed this for [url=http://www.nfa.ca/journalist/dewat.html:69ec5]Canada[/url:69ec5]
thats still a nice piece. theres a japanese company called marushin, who specializes in making replica, blank firing weapons like the mp40, thompson, m1 carbine, m16 etc, you can find them on ebay, but theyre expensive as hell. the one on this link appears to be much less expensive though.
type in the word 'marushin' and you should get alot of that stuff on ebay or anywhere else.
DEWAT, in Canada, comes from the term DEactivated WAr Trophy, basicly, an enemy weapon captured during a time of war, and deactivated. Now it means any deactivated weapon that cannot fire any kind of round, including blanks.