MacBook Air 11.6" Screw Size
Do you know what size 5 point torx screw is used? Is it smaller than a T8?
The bit you are referring to is not the same as the "star" shape screwdriver in our 54 Piece Bit Driver kit. iFixit is currently not a vendor for the 5 point security torx screws seen in the 2010 MB Air teardown.
To clarify the other answers here, vendors for that bit are required to do have customers do the following: "In order to purchase these bits you will need to sign a letter stating that you are an authorized serviceperson for the equipment where TORX Plus® tamper-resistant screws are used." From a rough search, it seems that many vendors within the US (such as the one mayer linked) do not actually enforce this rule, which would make the bit easier to acquire, and somewhat nullify the intended security aspects.
In its current "catalog," ifixit is claiming that you need a P2 for iPhone, P5 for Macbook Air, and P6 for Macbook Pro, so I'm pretty confused, but I'm leaning toward the answer posted here, which agrees with what kctool.com says.
I have a lot of respect for ifixit, but I think they made a mistake and should correct it, or if not, then they should clear things up to avoid this uncertainty.