You will need to get creative. Find a friend who has internet, and use a USB memory stick to move the stuff from there to your machine. If I were you I would get every app you think you must have all at one session on your friend's machine.
If you have an android phone you can download to it, use the USB charger cord to connect the phone to the linux box, then move what you need from phone -> CentOS.
A lot of linux support sites will send you a CD/DVD with everything on it. Costs are small, but it takes a while to get the CD in the mail see this website on somebody else's machine:
Download - CentOS Wiki You can get all of the RPM's and the distro on one DVD