if there is no software package that you need in a normal repo, try to find on AUR (Archlinux User Repository). AUR url-link : http://aur.archlinux.org
1. First download Tarball from packages URL
Download on tarball, then save. Go to downloaded files on terminal.
2. Extract the packages
$tar -xvzf packagesexample.tar.gz
3. Build packages
if you want to automaticly resolving the dependencies you can add -s option.
The packages will be build
4. Install the packages
Login to root user
#pacman -U *.pkg.tar.xz
To easy download from terminal, you need install wget first
$sudo pacman -S wget
For the example of installation, see below "installing xarchiver"
1. Downloading the tarball
2. Extracting and cd into the extracted folder
3. Then makepkg -s
4. Wait until package is created, at the end must be like this.
5. And finally installing the package, by typing sudo pacman -S *.pkg.tar.xz
And application is installed, enjoy. :D