There's no elegant solution
There are a few ways "to cast a spell or manifest a power that provides a +4-or-greater bonus to AC that lasts hours/level or longer, and have it apply to touch attacks." Unfortunately, because none of them were intended to do quite that, they're all very powerful options that happen to be able to provide a +4 touch AC bonus, but also do much more powerful things, which might make DMs somewhat leery. The easiest way to do this—and ultimately the solution I recommend—is to talk with your DM and homebrew something, or at least ask them to let the feat Deflective Armor apply to mage armor.
Fabricate and Wish
The solutions that cleanly meet your request are fabricate and wish. They can both create armor that does what you want (without the need for Deflective Armor), and both last longer than hours/level. In fact, they're both permanent.
The nonmagical property riverine (Stormwrack 128) applies half the AC bonus (rounded down) of any armor or shield as a deflection bonus (which then applies to touch AC). So a suit of riverine full plate will apply the requisite +4. The spell fabricate could create this riverine armor, since it's nonmagical, though do be aware that riverine adds a whopping 25,000 gp to the price of heavy armor, and you'd need to make a Craft check as per fabricate, along with 13,000 gp worth of riverine. Riverine has the advantage of being made of force, which sounds like it might be important for what you're trying to do.
Funnily enough, wish can't create the nonmagical riverine full plate, since it has a price over wish's 25k mundane item limit (though it might be able to create +1 riverine full plate...). It can, however, create a suit of +4 ghost ward armor. The ghost ward property (MIC 11) is a +1-equivalent property that allows magical armor to apply its enhancement bonus to touch AC. This will cost somewhere north of 6,000 xp, but if you're slinging around wish that shouldn't be too rough.
The problem, of course, is that both fabricate and wish break the game fairly trivially by generating wealth, which is precisely what they're doing here. Given the relative simplicity of breaking 3.5e's economy—the spell flesh to salt does so easily, for example—the best solution is to talk with your DM about how you intend to use these spells, and more importantly how you don't intend to use these spells. At the end of the day, getting +4 AC vs. touch attacks isn't particularly game breaking.
Persistent Spell is an infamous feat from Complete Arcane (81) that changes the duration of a spell to be 24 hours. It makes a spell cost a slot 6 levels higher than normal, but there are ways to offset those costs (notably Complete Divine's feat Divine Metamagic). This is a very powerful trick, though certainly playable at tables with mid – high optimization levels.
Persistent Spell opens up a few answers to your question that didn't meet the "lasts hours/level or longer" stipulation, like holy star. I think the standout here is armor of darkness, a domain spell from the Spell Compendium. Like mage armor, it creates a magical armor effect, and adds a deflection bonus to AC, which applies to touch attacks. You'd need a feat like Ocular Spell (Lords of Madness 181) to cast it with Persistent Spell, but a character like a Nightcloak of Shar with Divine Metamagic, Ocular Spell, and Persistent Spell is a pretty thematic and cohesive character based around vision and darkness; thematic strength often matters quite a lot when getting a DM to allow a powerful option, but again, just like with wish and fabricate, Persistent Spell can be very tricky to balance, so talk with your DM about it.
Some possibilities that don't quite fit
A 2nd level Wilder gains the ability Elude Touch, allowing their CHA bonus to apply to touch AC, capped by regular AC. This means that, if a Wilder has sufficient charisma, inertial armor increasing her regular AC (and thus the cap on Elude Touch) will also increase her touch AC. Of course, there's little reason for a Wilder to manifest inertial armor rather than just wearing armor.
If it's the "instantly creating armor" part you're looking for, a ring of arming (MIC 122) will summon armor immediately to you, though you still need to get your hands on armor that applies to touch AC, whether that's riverine, ghost ward, or Deflective Armor.
At the end of the day, I think your best bets are either getting your DM to let Deflective Armor apply to mage armor or to go with riverine armor, possibly with a ring of arming if "armor up as a standard action" is important to you. I will say that Persistent Spell can be fun in a campaign that's high enough power level, but it's more of a commitment of your character's build, so might be a less desirable solution.