For future reference, you can just download the packages from archives (in this case, Debian's, but they should work on Ubuntu as well):
Quote:
wget http://archive.debian.org/debian/pool/main/g/gtksourceview/libgtksourceview-common_1.8.3-1_all.deb
wget http://archive.debian.org/debian/pool/main/g/gtksourceview/libgtksourceview1.0-0_1.8.3-1_i386.deb
dpkg -i *.deb
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