I assume old style 360, though with the newer ones being internal I do not know why I asked.
Anyway just pulled one off one of the stash of 20 gig drives (
http://gbatemp.net/threads/uk-gamestations-360-20-gig-hard-drives-for-a-fiver.323257/ ) and it was just a piece of metal foil stuck on with double sided tape. The important part though is it was not any kind of attachment with tags or custom shapes or anything. I don't mind sorting out a proper cad file if you want but I am not sure there is much point as there are quite literally just three dimensions and you would be wanting to sort text anyway, even if you have never used 2d CAD before then you could probably figure it out by looking (
http://librecad.org/cms/home.html is a decent free one,
http://www.3ds.com/products-services/draftsight-cad-software/features/ is also nice and will definitely do industry standard DXF).
Were I making one for myself it would probably be etched electronically
You might be able to do it with a laser, if you fancy playing with a stencil that any tshirt supplier could make you (loads will have a custom cutter they can feed some sticky back plastic into) and a chemical etchant then that is an option* or if you are not using metal (again it is just a 2d shape so anything that fits and can be made reasonably thin will do) you have many more options.
*I reckon a copper foil one would look pretty nice and etching copper at home is something loads of electronics people do.
I am not sure where you would find either a metal etcher or a metal cutter that will not charge you the silly money for a one off (by which I mean £20 or so, doing more will probably be a lot less) and I certainly don't know anybody specialising in it for 360s. I am not geared for it right now really or I would make a punch for myself and send some blanks your way (or the punch if you have a vice or press or something you can use for yourself).