TL;DR: Druids and sorcerers have access to feats that offer Rage-like effects, while the Touchstone and Planar Touchstone feats offer access to a smorgasbord of effects, including Rage-like effects.
The best of them is the Catalogues of Enlightenment Planar Touchstone, which gives the granted ability of any cleric domain – the Passion Domain gives a 1/day self-only rage spell, which is explicitly “otherwise identical to a barbarian’s Rage.” This is the only feat option I could find that might qualify as Rage for the purposes of prerequisites.
White Dragon Lineage [Draconic]
Dragon Magic has a number of feats for sorcerers to explore the draconic origins of their magics. For 3rd-level sorcerers who have taken Draconic Heritage (white), White Dragon Lineage is a feat that allows you to expend an arcane spell slot to get temporary HP and resistance to cold equal to 5× the spell level, lasting for 1 + Cha rounds. It’s explicitly like a barbarian’s Rage but is not Rage for prerequisites.
Wolverine’s Rage [Wild]
This feat from Complete Divine allows a druid to expend a daily use of Wild Shape to get +2 Str, +2 Con, and −2 AC for 5 rounds after he or she has been hurt. Again, this is not true Rage for the purpose of prerequisites.
Sandstorm has a feat, Touchstone, and Planar Handbook has a related feat, Planar Touchstone, that allow you to get one of many different powers by visiting certain historic or magical locations. These two feats are incredibly versatile, and can get you a lot of stuff.
Catalogues of Enlightenment (Planar Touchstone)
A planar touchstone option, the Catalogues of Englightenment have as its base option “Choose a cleric domain; you gain the granted power of that domain.” There are a lot of cleric domains, and several of them have options similar to Rage. The problem is, the Catalogues don’t specify what to treat your cleric level as if you aren’t actually a cleric. The most reasonable answer is to use your character level, but square that with your DM. Note that the Catalogues of Enlightenment are considered an 8th-level encounter, so you may not be able to put this in your backstory.
Passion Domain (Eberron Campaign Setting)
For a total time per day of 1 round per cleric level, as a free action you can act as if under the effect of the rage spell. This granted power is a supernatural ability.
The effect is otherwise identical with a barbarian’s rage
Doesn’t get any more direct than that.
Retribution Domain (Spell Compendium)
Once per day, if you have been harmed by someone in combat, you can make a strike of vengeance with a melee or ranged weapon against that foe on your next action. If this strike hits, you deal maximum damage.
Strength Domain (Player’s Handbook)
You can perform a feat of strength as a supernatural ability. You gain an enhancement bonus to Strength equal to your cleric level. Activating the power is a free action, the power lasts one round, and it is usable once per day.
Fluff is off, but the effect is pretty similar.
Wrath Domain (Spell Compendium)
Once per day, you can subtract a number of points from your Wisdom score equal to or less than your cleric level. For every 2 points you subtract from your Wisdom score, add 1 point and add them to your Strength score. You suffer all the effects of reduced Wisdom, including access to spells and bonus spells, reduction of Will saves, and penalties on Wisdom-based skills. This trade between ability scores lasts for 1 round per cleric level and cannot be ended prematurely.
Hatred Domain (Spell Compendium)
Once per day as a free action, choose one opponent. Against that foe you gain a +2 profane bonus on attack rolls, saving throws, and Armor Class for 1 minute.
More like Favored Enemy than Rage, but eh, might work.
Destruction Domain (Player’s Handbook)
You gain the smite power, the supernatural ability to make a single melee attack with a +4 bonus on attack rolls and a bonus on damage rolls equal to your cleric level (if you hit). You must declare the smite before making the attack. The ability is usable once per day.
Possibly more like Smite Evil, but again, might work.
Sunken City of Pazar (Touchstone)
For beating this 4th-level encounter, you get Powerful Build 1/day for a minute. The higher-order version makes it last for 8 hours. Powerful Build makes you behave in many ways as if you were larger, which replicates a lot of the functionality of Rage.
Pyramid of Amun-Re (Touchstone)
6th-level encounter, you get temporary hit points 1/day for an hour (24 hours as the higher-order version). Still, seeing as it requires a Concentration check, not that similar to Rage in fluff though the concept of temporary hit points is very much in keeping.
The Life Molds of Neumannus (Planar Touchstone)
The fluff is completely different, but the higher-order ability (i.e. needs recharging) of this planar touchstone (a 12th-level encounter) is an ability to temporary gain a bonus to strength, as well as DR 5/adamantine, resistance to fire and acid, and a penalty to Dexterity by becoming more construct-like.
Densahl’s Challenge (Planar Touchstone)
The higher-order ability of this 13th-level encounter is a temporary damage boost equal to your character level. You get to choose to use it after learning whether or not you hit, which is nice, though the damage is low for something you get so few uses of.