This question is geared more towards the Commander deck help forum, not the Rules Q&A.
There's no card as similar to Blade of Selves, because myriad is a fairly new ability still. There's Assault Suit, which sort of acts the same way, by giving your commander more opportunities to swing at opponents.
January 6, 2017 7:16 a.m.
It is also worth noting that Blade of Selves copying your commander, will cause you to legend rule the copies meaning they won't hit anyway. If you want to take out more than one person at a time, you'd be better off using extra turn or extra combat strategies, although those require blue or red generally. Examples include Time Warp and Aggravated Assault. If you are really set on blade of selves though, there is Mirror Gallery but the copies still will not do commander damage as that is an intrinsic ability of your commander. (basically only the card that can go to your command zone can do commander damage). Barring all that you will simply have to wait through the turn cycle, in which case its best to make sure your commander is well protected from removal.
January 6, 2017 11:12 a.m.
Everything that reads "each opponent" i would guess? There are pretty neat discard things around or things like Impact Tremors.
January 6, 2017 noon
What colors are we talking? There's a lot of effects that can help you to handle multiple opponents, but it all depends on what colors you have at your disposal.
As has already been stated, if your plan is to win via commander damage (as it almost certainly is in voltron), what you'll most likely need is extra turns or extra combat steps, as copies of your commander won't inflict commander damage, and non-combat damage won't either.
January 6, 2017 2:09 p.m.
Aggravated Assault + Sword of Feast and Famine can combo out and win. If you're not looking for infinite combos, Aggravated Assault is still a perfectly good card. I'm also quite fond of World at War, Savage Beating, which at instant speed can kill unexpectedly, and Waves of Aggression.
Those are just a few suggestions off the top of my head.
January 6, 2017 3:36 p.m.
Thanks, Thanatos! I didn't think there would be a card exactly like Blade of Selves, but I was looking for something that would have a similar effect, and you provided me with just what I needed.