You're not asking for an advise, do you?
Just bragging like a puber.
Well, I'll help you for your future braggings.
Lower down your dimensions, so that they are believable or in anyway possible.
Your 12"x7" has the double volume of a 9"x5.75" (an enormous dick) or an 8"x6" (still enormous )
What you are suggesting is that you have 2 of such dicks before pumping.
So no there aren't such cylinders for pumping those dicks.
Try again...