Feats or Magic Items to boost a Marshal's Aura?

[Kantolin]

Do any such feats or magic items (or spells) exist?

[ZeroNumerous]

The Helm of Tactics gives a +1 boost to a minor aura 3/day.

The Horn of Resilience increases your major aura by 1 3/day.

Other than that, I got nothing.

[CASTLEMIKE]

Standard Cloak of Charisma. Candle of Invocation to get a Genie like an Efreeti or other outsider to Grant Wishes.

This would depend on the game and the DM: Take a level of Dragon Shaman and acquire a Fiendish Symbiote from the Fiend Folio if it will let you learn an additional aura like it does for spellcasters and get a Minor Aura like Motivate Charisma. Possible learn a Minor Aura in a Major Aura slot for Marshal this way to.

[Kantolin]

I think the two magic items sound more like what I'm looking for.

Where are the Helm of Tactics and Horn of Resilience found, however?

I do plan on boosting charisma, can't really dip into dragon shaman, and don't have a desire to utilize candles of invocation. Thanks, though.

[ZeroNumerous]

Magic Item Compendium.

[Keld Denar]

Scarlet Prism (or some other red color) Ioun Stone increases the value of all martial auras by 1. I believe it has a cost of about 30,000, on par with the +1 CL stone. I don't have the source, but one of my friends just crafted one in Living Greyhawk, so it must exist somewhere.

[AtomicKitKat]

Fiendish Codex 2. Dilate Aura. Once per encounter, double the radius of an aura(presumably, once per encounter per aura).

[SpikeFightwicky]

There's a feat in the Fiendish Codex II -> Dilate Aura (pg. 83) that increases the range of an aura ability. I think it's by 20 or 30 feet.