For a lightning blizzard, use the lightning shield model, or maybe the lightning bolt doodad model. An old, very old, version of Dota had a revenant hero with electric attacks (much like the current Razor) that had an electric blizzard for an ultimate. That's how they did it in that.
I think the reason the chain lightning effect isn't working for you is that that bolt of lightning wants to be an instant attack, and shockwave needs a missile. If you can take advantage of projectile scaling and use a smallish unit for the caster, you could use the farseer missile model, and scale it up by a factor of two to get something the right size for a shockwave.
There are probably other lightning-y missiles in the game. Just don't try to use chain lightning.