Normally it is surprising how little it matters which kernel you are using.
If you can live with not getting automatic security updates and don't want to compile the kernel yourselv there is no guarantee that this will really work.
But there is a high probability that you can use a -rt kernel from unstable/testing or even from a different debian-based linux distribution like one from here: http://kernel.ubuntu.com/~kernel-ppa/mainline/?C=N;O=D
Kind regards,
Gunter.