I avoided purchasing one by forming a loop with the wire. I cut a 20cm (8in) piece, then I tie a triple knot (the simple over hand knot with both ends). The wire is very slippery so I move the first knot as close to the ends as possible, so as not to waste floss.

Having a loop allows to have a firm hold on the floss and adjust tension. I use it with both hands though. And I waste very little floss because I can rotate the loop and use every inch of it.