I'm actually working on my Yoko gun at this moment
I used PVC pipe from Lowes for the base and made most of it out of cardboard, i went and bought a plastic gun to use for the trigger.
As soon as i get back from vacation i plan on painting it and posting a tutorial when its done (I leave tonight so that'll be around 1 week to 1 1/2 week) I'll post here again with a link to my livejournal when i post it
Hopefully i'll be more help at that time
PM me if you need help before then, i'll try to get some before painting pictures up tonight