AV magic items you can use when you score a crit:
Flame Bracers
Trauma Bracers
Assault Boots
War Ring
Stalwart Belt
Solitaire(all of them)
Flame Bracers: The problem is, they don't really outperform Iron Armbands of Power. If I hit on 10-20, I deal 2 damage 50% of the time the the armbands. If I only do extra damage on a 19 or 20, I average 3.5 damage 10% of the time

and the paragon item is not much better, and too expensive right now anyway.
Trauma Bracers: can't find it. You mean Trauma Shield? Seems to be one of those utterly useless items the AV is cluttered with, no property but a crappy daily that's useful once in a lifetime.
Assault Boots: This is not bad, (knocking targets prone on a crit) but I already have plenty of knocking prone tricks, and I rather not give up the boots of adept charging. The boots are crucial, because after a charge I want to step back and let the guys come closer so polearm gamble triggers.
War Ring: Gives only 1d6 extra on a crit for the Jagged Weapon
Stalwart Belt: gain temp HP on a crit - I'm already getting enough temp HP left and right. They don't stack, so I rather not add more sources.
Solitaire (Cinnabar): roll a save on a crit: It's good, but since I'm a dreadnought those save ends effects are already gone before my turn even starts
Solitaire (Citrine): spend healing surge on a crit. This is good. I'll take it when I can afford it. It's level 11.
Solitaire (Aquamarine): free attack after a crit. Awesome. Stacks with Rampage. It's level 16, but I'm going to get it.
Thanks for the tips!