This is easy depending on where you live. If you are in the US, still have to wait longer for this.
I do not work for but I am a sponsored driver by MTroniks. MTroniks makes water proof ESC's and RX's. The US importer is:
Now in the US they use 75MHz for their land frequencies. MTroniks is coming out with a 75MHz water proof ESC but it has not been released yet and I do not have the time frame for it. But Hobby People do carry any of the ESC's that MTroniks currently sells.
Hope this helps some.