Fourtreks makes a whole series of mounts. I have the HiLift mount and the twin tool axe/shovel mount. As Mark says, they're not cheap. Also, they don't lock... I use a steel cable and weather proof padlock for mine.
I have the Demello Hi-lift mount and just bought the FourTrek PullPal and Shovel/Axe mounts. All of them are pricey, but very well made. Use a cable lock for the Hi-lift and PullPal and it would be nice to be able to lock the ShovelAxe in place too.