I had that happen at work. We had dozens of spare floppies from old computers and I figured I'd save $20. Opened it up and was surprized to see no mounting hardware. I took the ghetto route. Found a piece of scrap aluminum, drilled two holes, and mounted the drive myself. Took maybe 3 minutes to do if you have a drill. One hole for a screw on the floppy drive and one hole for the mounting bracket on the CD drive mount right above it. The floppy is stable with just one screw since the case front is a slot that holds that portion steady.
By the way, as I did it I realized this is great proof that I was a computer geek (didn't need proof but it was an interesting thought).