do you want it just for the outfit or do you wanna play airsoft with it?
if its just for the looks then try to get a cheap china knockoff somewhere
http://www.wgcshop.com/wgc2008/main/pro ... atid=&cat=or maybe there is a springer version which might be even cheaper...
if you want to play with it then keep in mind that gasguns dont work well in cold weather
otherwise there is just the AEP battery powered route via tokyo marui
which is underpowered in my opinion...
you should be able to mount a sling on it..it has mounts
i even have a gutted mp7 here that i dont need
but dont know if its possible to ship to USandA without too much hassle(hoff)