Comment 29 for bug 281610

you can find old builds of xserver-xorg-core by following the links for your architecture at the bottom of

https://launchpad.net/ubuntu/+source/xorg-server/2:1.5.1-1ubuntu2

(for instance, this could lead to
https://launchpad.net/ubuntu/intrepid/i386/xserver-xorg-core/2:1.5.1-1ubuntu2
and finally
http://launchpadlibrarian.net/18263189/xserver-xorg-core_1.5.1-1ubuntu2_i386.deb
)