I don't recall having ever seen a front mount flail mower but if you do a search on the internet you will get some hits for them - two I found were Trimax Mowers (www.trimaxmowers.com) and Agritek (www.agritek.de). The Agritek site has pictures of units mounted on the Kubota F60 series but not on the older F00 series. Unfortunately neither are North American companies.
If you are really serious about a front mount flail mower my suggestion would be to convert a 3ph unit to front mount. This is what I did to get a tiller for my F2400. It is quite a simple process. You need to cut off the 3ph connections and make mounting arms to fit you sockets (I used 1" x 2" steel tubing). Turn the gear box over so that the input shaft faces the rear of the unit and mount a 2:1 reversing reducing gear box on the input shaft. This will give you the right rotation and velocity when you engage your PTO in low range (1100 rpm). If I had a use for a flail mower, I would try this myself. /forums/images/graemlins/laugh.gif
Good luck.