I'm not positive but your best bet is probably the Raptor 350 pegs, which if they fit would work out nice since they're basically the same as the yfz450.
As far as I know, no other pegs will fit. I made my own wide pegs by getting an old set of warrior pegs and bolting them to mine. Worked really well until I got my IMS pegs. Here is a pic of what they looked like.
Click to enlarge
I just finished up a set of wide pegs for my sons Warrior.
I used a set of YFZ pegs and welded them on the factory warrior mounts. Just got 'em primed and ready for paint tomorrow.
As far as I know, no other pegs will fit. I made my own wide pegs by getting an old set of warrior pegs and bolting them to mine. Worked really well until I got my IMS pegs. Here is a pic of what they looked like.
Click to enlarge
This is just about the cheapest and most economical way to get a wide peg. You can find a set of extra foot pegs on ebay for under 20 bucks, cut the mounts off and bolt em up