I don't know the distro you're using and my answers may not be 100% correct, but I'll try to help. I assume your distro uses RPMs (it's hard to confirm this using the website) - you know what kind of packages you use
When it comes to RPMs, using packages for a differenet distro won't work in most cases (there are distro-independent RPMs, but rare). So you can probably use only thizlinux site (or their mirrors - if they have them).
There's a nice site with list of apt-get sites: www.apt-get.org
but it won't halp you much, I think. You can enter the sites and probably even download packages, but they won't be installed.
Just a reinstall of aptget and/or synaptic won't change this. The problem is in the packages currently installed by the distro (thir dependencies and so on).
If I am right, the options for you are to upgrade using thizlinux site and/or install binary versions or compile from source if you want to have software not provided in the distro.