Go to www.ifixit.com and look at the take apart instructions for your MacBook Pro. You might be able to find out what that part is called from there.
Maybe something at:
http://www.welovemacs.com
http://www.powerbookmedic.com
BTW: Is it broken or ????
It looks like one could be made from some scrap plastic or even with a hot glue gun and hard glue stick and a drill.
- Patrick
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It's missing
- Tomás M
The OP is from Chile, SA. Probably no Apple Stores there but maybe an authorized Apple service repair? It doesn't appear from his IP address that he's near a large metro area.
Particularly as the 1278 model was first released in June 2009!