marker

Looking for a second marker since the cs1 on the horizon, I would be interested in geo 2's & 3's, could push to a lv1 or anything down too a ego 9

I have recently bought a Bt sa 17 pistol and I was wondering whether I can use at Delta Force (in Upminster to be precise). The gun itself uses 12 gram co2 cartridges. I know Delta Force say that they don't allow you to bring your own marker on their website but I was reading a post on this...