I have created a backport of aircrack-ng based on the version in Jessie/Testing. This may be installed with the command:
dpkg -i aircrack-ng_1.1-6~bpo70+1_amd64.deb
(remove the package with command: dpkg -r aircrack-ng)
download here

This package is now available in Debian wheezy-backports.

Back in March 2012 I built the latest svn version from source, available here.
I have included the necessary scripts and binary files in the ‘bin/’ directory. Copy these to somewhere like: /usr/local/sbin/