To be able to use grsecurity optimally you need to compile your own kernel.
Search the "Kernel HOWTO" and start reading.
Then get the kernelsources from Ubuntu and try compiling your own kernel based on your current configuration.
Then try to get a "vanilla" kernel from
www.kernel.org, try to configure and compile it.
If you can get a working kernel you are ready for the next stage:
Try patching the kernel with the Grsecurity patch (try the latest test-patch on the vanilla kernel with the same number).
Read the Grsecurity documentation and try to get it working.
And don't forget to read most (all) information on grsecurity and pax you encounter while configuring the kernel.
It will cost you quit some time.
You could try to find a precompiled kernel, but IMHO that would be a suboptimal solution.
It might be safe, but possibly the most important options might be missing.
If you know anyone who has experience in compiling kernels, let him demonstrate it to you.
Building your own kernel works easier if you have a working start point.
A demonstration saves you hours or even days.