yes! i was so sad there weren't any TTGL characters, i think i was the only one cosplaying a new spring anime this year, period. you are my hero.
but i dunno. there might be some sort of gun-making tutorial on the cosplay.com forums; i know there's a guy on there who can make anything out of cardboard and hot glue, and conventions sometimes have workshops on making props out of foam. i'd make the gun barrel out of pvc pipe, just so it's got something sturdy to start with. i wanna see this gun when you're done with it... and your costume...