Originally Posted by Drake
You can get silicone oil at any R/C or hobby shop (ask for 100% silicone shock oil, pick a very light weight one).
For CO2 you can also use (and I actually recommend) Crosman Pelgun Oil, which you can get wherever they sell pellet guns I guess. It's better formulated to handle Co2 than just silicone oil, which is used with propane) and will help protect your seals and avoid leaks from developing.
And where do I apply it on my gun? This will be my first GBB airsoft gun.