We usually find a 1.5 mm flathead screwdriver bit (or whatever size is slightly larger than the distance between two lobes furthest apart from one another) and file it down until it fits in there. It's a bit easier to remove the screws if you push down on the screwdriver when you initially break the screws free (takes some preload off the threads).

try find them on ebay.

Looks like very limited availability :) http://www.traderscity.com/board/product...

and http://www.8starshop.com/en/12-in-1-comp...

Check this question has more answers for you http://www.ifixit.com/Answers/View/39838...

Here's how I thwart safety screws, though I dunno how well it will work in your situation; the Torx Plus screws on an iPhone are smaller than the screws I've tried this with before

You'll need a hard plastic pen (Like a Bic Cristal) and a source of heat, but preferably not an open flame. Remove the ink cartridge and ballpoint; you're not going to need them for this.

Basically, the idea is to melt the plastic so that it becomes pliable enough to flow into the screw-head, cool, and act as a temporary screw-driver.

If you're going to be working with a particular type of Security Screw often, I recommend tracking down a proper set of drivers for it. But if this is just an exotic screw type that you encounter only so often, this makes a pretty good stopgap solution. I've used it to beat Security Torx, TP3's, and Tri-Wing screws when I encounter them.

The only thing I wouldn't recommend using it on is Spanner (Snake-Eye) screws.

These screws are pentalobe screws, to open it and to put in standard phillips ones, get iFixit's iPhone 4 Liberation Kit.

The correct tool to remove the pentalobe screws is the IP2466 tool. I found this info while sourcing the same question.