Just use the built in one, in the wifi settings menu , just "search". If It can't find any, it's out of range, 10 meters.
I don't think we want this kind of thing discussed here. If you had a legitimate reason for needing a mac address you'd be able to get one.
...I'd check a homebrew site. At some point I obtained one that supposedly could...but it was a WIP and couldn't even find my router I know the psp has a tool...oh and I can't remember the names of these, best thing to do is look in the applications range of quickjump.net