Set screws are 6mm diameter with a 1mm (coarse) pitch and 6mm in length if your local Ace Hardware has an awesome set screw inventory. In a pinch, you can make your own if you are handy with a hacksaw and a file (next to impossible in my case but maybe not in yours!).
I would probably follow Eli's suggestion and just tough it out with 3 until the replacements arrive.
BTW, welcome to the FOG!
