If you want the official Ubuntu stock kernel (not a mainline kernel) from an unsupported version, see below.
For differences between Mainline and Stock kernels see https://askubuntu.com/a/91374/555474
I had to install an even older kernel (2.6.32.21-generic) for stock modules to work with a custom kernel. No hardware was working, so I had to download manually.
Here is how to obtain the discontinued kernels manually from http://old-releases.ubuntu.com/ubuntu/
Essentially you will need the kernel's headers for your processor, common (all) headers, and the kernel image for your processor.
- In the steps below, replace - x.x.xx-xxwith your kernel version and- amd64with your processor type. Note this is for the generic kernel and not using extra features such as PAE.
 
- Go to http://old-releases.ubuntu.com/ubuntu/pool/main/l/linux/ (I believe this lists most if not all the old kernel packages) 
- In the page CTRL+F find headers-x.x.xx-xx-genericand download the
- linux-headers-x.x.xx-xx-generic_x.x.xx-xx.yy_amd64.deb
- linux-headers-x.x.xx-xx-generic_x.x.xx-xx.yy_all.deb
 
- In the page CTRL+F find - image-x.x.xx-xx-genericand download the
 - 
- linux-image-2.6.32-21-generic_2.6.32-21.32_amd64.deb
 
- Put all of these packages in a folder alone, and from that folder (- cdinto it) run
 - 
- sudo dpkg -i *.deb