I want to use the second monitor "vga-0" with resolution 1440x900, but in display->size and orientation the desired resolution is missing. What shell I do? Thank you.

If you're using the Nvidia binary driver you could try nvidia-settings

No, I am on radeon driver, and I do not have xorg.conf file. anyway, resolutions are stored in some kde file, I used to add it manually before, but now I can not find it.

BTW, running
xrandr --newmode "1440x900" 106.5 1440 1520 1672 1904 900 901 904 932 -HSync +VSync
xrandr --addmode VGA-0 1440x900
xrandr --output VGA-0 --mode 1440x900

results in complaints about maximum screen size 1400x1400 and subsequent screen freeze.