Anthony, I think many 5 1/4" floppy drives actually have a different connector than a 3 1/2" drive, so you may not even be able to connect it to your motherboard.  I could be wrong about this, but you should probably check on that before you do anything.
Of course I wouldn't doubt that somebody has made a converter.
A couple of other options if you can't find a converter would be to look for an old cable that has both connectors on it (I can send you one for the price of shipping if you want!!) or get a combo drive that has both 3-1/2" and 5-1/4" drive in a single 5-1/4" frame with a single 3-1/2" connector and power.