I've never seen a really long torx screwdriver at a store that will reach all the way down inside the handle of a compact Mac. Only pictures of them.

It's sometimes easier to find the right size bit, then put some extensions on it to reach all the way down in the handle. That's what I do. The bit itself should probably be the 3-inch long kind (or longer is obviously OK), then you can just take an ordinary 1/4" socket to it.