need a small wall vent attachment, where can i get?

i have a computer server cabinet that needs to be vented ot the outside as it heats the room up and gets too hot.
what i want to do is put a small inline fan in the roof and run a pipe, about 50mm in diameter, down the interior wall cavity of the room which is made from 90x45 pine with gyprock on each side and have it come out the wall with some sort of outlet on it so i can plug a flexible pipe into it like a vacuum cleaner pipe so it can suck all the hot air out into the roof.
but i have no idea where i can find an adaptor that i can mount in gyprock to allow this.
i can get up inside the gyprock wall as i have a cutout for network connections where i have a plate installed to plug cables in so need something i can mount in the wall a bit higher up to enable me to plug a hose into.
any ideas what i can use??
http://img233.imageshack.us/img233/5944/venti.jpg


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