I have also been thinking about getting one but i have never used one so I wouldnt know how they work. I have not been able to find one for my mower. Its a 36 inch wright velke walkbehind...If any one knows where to get one please let me know.
I don't know if there are ones for a larger walk behind like you have, but I have seen people that get a pipe and fill it with gravel or sand and attach it, it's a cheaper way to do it, and if there are none for your mower, you could do that.