Nitrogen filling spheres

Hello,

I'm not from England. Sorry for my bad English. I'm interested in the mechanics and automotive. I would like to know if anyone has done a device for punching spheres of nitrogen. Looking for the device but can’t find in order to make yourself. Maybe someone would have shared the idea. I do not know what section to put.
I have a Xantia 1.8 16V.

Regards dudus