yes there is, here is a pic of his co2 refillable mags for the we m4 awss.
its just a standard we co2 mag but instead of using a disposable co2 capsule he used a capsule with a filling hole on the side. but since the refillable capsule does not have a valve up top. he drilled a hole on the side so he can quickly refill it with co2 from his main tank.