Maybe you are doing something wrong if omastar isn't working... it probably isn't doing well because
a: there are a few pokes that share weaknesses (namely kabutops and weavile)
b: it isn't setting up rain on it's own
c: life orb recoil and too offensive spread make it's base 125 defense seem poor.
I suggest you give it more HP Evs. 252 speed is rarely the most efficient speed on a swift swimmer. 208 speed Evs allows you to outrun Aerodactyl, Crobat and Jolteon. If you don't care much for them, then 160 speed EVs outruns sceptile, alakazam and other base 120s. 140 speed outruns starmie, azelf, etc. I wouldn't go any lower than 351.
I use leftovers and HYDRO PUMP, with 362 speed. It gets the job done. Put the rest in HP because it will help it's physical defense more than defense Evs themselves. This is because omastar has poor HP compared to it's defense. If you don't think leftovers will help, stick with mystic water, wise glasses, or a chople berry or ground weakening berry.
I suggest not always blowing electrode up. It could come in handy later. Try to switch around to a resist after rain dance is up. Say there is a pokemon using ICE SHARD on electrode. You could switch in omastar and start to kill.
If they were using SURF on you (say a swampert afraid of ghosts) then switch in LUDICOLO. It is common sense, really. I say get thunder over taunt but I have never used electrode before. What sort of things do people try to do to electrode?