I recently acquired a 2004 50th anniversary american deluxe strat, but it didn't come with it's stock tremolo bar. A spare that I had at home doesn't fit, however the Floyd Rose threads will fit, albeit far too big of a bar for the smaller Fender bridge. Can anyone tell me what arm I need to be looking for so I can get this replaced?
Take it to a music store and tell them you need a tremolo arm. I've never seen a music store that sells guitars that also didn't have a few lying around, or replacement arms on a rack, usually made by Allparts.
Hmmm...I wonder what this button does...
i would just order one from MF if you are in the US. free shipping and no tax, and you don't have to drive to a music store.

that is what i do.