Panel mount flange for rerouting cables

[s0rce]

On many cases now there is a round rubber flange that can be used to route cables from the back back into the inside of the case (ex. to use the esata as an internal sata, etc). I want to add one of these to a mini ITX case for my server.

You can see them for example on the back of the Antec Lanboy air. I was wondering if any one know where to buy these little rubber/plastic things so I could add one to the back panel?

Thanks,
s0rce

edit: they are called: bushings